Clemente’s professional baseball career began when Pedrín Zorilla offered Clemente, 18, a contract which he signed on October 9, 1952, with the Cangrejeros de Santurce (“Crabbers”), a winter league team and franchise of the Puerto Rican Professional Baseball League (LBBPR). He was a bench player during his first season but was promoted to the Cangrejeros starting lineup the following season. During this season he hit .288 as the team’s leadoff hitter.

After signing with the Dodgers on February 19, 1954, Clemente moved to Montreal to play with the Royals. Affected early on by both climate and language differences, Clemente received assistance from bilingual teammates such as infielder Chico Fernandez and pitchers Tommy Lasorda and Joe Black.

Clemente’s extra inning, walk-off home run of July 25, 1954, the first home run of his North American baseball career, was hit in his first at-bat after entering the game as a defensive replacement. Perhaps prompted by Sukeforth’s followup visit (“I don’t care if you never play him; we’re going to finish last, and we’re going to draft him number one”), Clemente’s appearance ended a nearly two-month-long drought starting on June 6 (17 appearances, 6 starts, and 24 at-bats in 60 games). From this point forward, Clemente’s playing time increased significantly; he started every subsequent game against a left-handed starting pitcher, finishing the season with a batting average of .257 in 87 games. Clemente would complement his July 25 walk-off homer with another on September 5, as well as a walk-off outfield assist (cutting down the potential tying run at the plate) on August 18, his 20th birthday. As promised, the Pirates made Clemente the first selection of the rookie draft that took place on November 22, 1954.

Clemente debuted with the Pirates on April 17, 1955, wearing uniform number 13, in the first game of a doubleheader against the Brooklyn Dodgers. At the beginning of his time with the Pirates, he experienced frustration because of racial tension with the local media and some teammates. Clemente responded to this by stating, “I don’t believe in color.” He noted that, during his upbringing, he was taught to never discriminate against someone based on ethnicity.

The following season, on July 25, 1956 in Forbes Field, Clemente hit the only documented walk-off, inside-the-park grand slam in modern MLB play. Clemente was still fulfilling his Marine Corps Reserve duty during spring of 1959 and set to be released from Camp Lejeune until April 4. A Pennsylvania State Senator, John M. Walker, wrote to US Senator Hugh Scott requesting an early release on March 4 so Clemente could join the team for spring training.

At the time of his death, Clemente had established several records with the Pirates, including most triples in a game (three) and hits in two consecutive games (ten). He won 12 Gold Glove Awards and shares the record of most won among outfielders with Willie Mays. On July 25, 1956, in a 9–8 Pittsburgh win against the Chicago Cubs, Clemente hit the only walk-off inside-the-park grand slam in professional baseball history.

In September 1958, Clemente joined the United States Marine Corps Reserve. He went on to serve his six-month active duty commitment at Parris Island, South Carolina, Camp LeJeune in North Carolina, and Washington, D.C. At Parris Island, Clemente received his recruit training with Platoon 346 of the 3rd Recruit Battalion. The rigorous Marine Corps training programs helped Clemente physically; he added strength by gaining ten pounds and said his back troubles (caused by being in a 1954 auto accident, see below) had disappeared. He was a private first class in the Marine Corps Reserve until September 1964.

The Pirates experienced several difficult seasons through the 1950s, although they did manage a winning season in 1958, their first since 1948.

Early in the 1960 season, Clemente led the league with a .353 batting average, and the 14 extra-base hits and 25 RBIs recorded in May alone resulted in Clemente’s selection as the National League’s Player of the Month. His batting average would remain above the .300 mark throughout the course of the campaign. On August 5 at Forbes Field, Clemente crashed into the right field wall while making a pivotal play, depriving San Francisco’s Willie Mays of a leadoff, extra-base hit in a game eventually won by Pittsburgh, 1–0. The resulting injury necessitated five stitches to the chin and a five-game layoff for Clemente, while the catch itself was described by Giants beat writer Bob Stevens as “rank[ing] with the greatest of all time, as well as one of the most frightening to watch and painful to make.” The Pirates compiled a 95–59 record during the regular season, winning the NL pennant, and defeated the New York Yankees in a seven-game World Series. Clemente batted .310 in the series, hitting safely at least once in every game. His .314 batting average, 16 home runs, and defensive playing during the course of the season had earned him his first spot on the NL All-Star roster as a reserve player, and he replaced Hank Aaron in right field during the 7th and 8th innings in the second All-Star game held that season (two All-Star games were held each season from 1959 through 1962).

During spring training in 1961, following advice from Pirates’ batting coach George Sisler, Clemente tried to modify his batting technique by using a heavier bat to slow the speed of his swing. During the 1961 season, Clemente was named the starting NL right fielder for the first of two All-Star games and went 2 for 4; he hit a triple on his first at-bat and scored the team’s first run, then drove in the second with a sacrifice fly. With the AL ahead 4–3 in the 10th inning, he teamed with fellow future HOFers Hank Aaron, Willie Mays, and Frank Robinson to engineer a come-from-behind 5–4 NL victory, culminating in Clemente’s walk-off single off knuckleballer Hoyt Wilhelm. Clemente started again in right field for the second All-Star game held that season and was 0 for 2, flying and grounding out in the 2nd and 4th innings. That season he received his first Gold Glove Award.

Following the 1961 season, he traveled to Puerto Rico along with Orlando Cepeda, who was a native of Ponce. When both players arrived, they were received by 18,000 people. During this time, he was also involved in managing the Senadores de San Juan of the Puerto Rican League, as well as playing with the team during the major league off-season. During the course of the winter league, Clemente injured his thigh while doing some work at home but wanted to participate in the league’s all-star game. He pinch-hit in the game and got a single, but experienced a complication of his injury as a result, and had to undergo surgery shortly after being carried off the playing field. This condition limited his role with the Pirates in the first half of the 1965 season, during which he batted .257. Although he was inactive for many games, when he returned to the regular starting lineup, he got hits in 33 out of 34 games and his batting average climbed up to .340. He participated as a pinch hitter and replaced Willie Stargell playing left field during the All-Star Game on July 15.

Clemente was an All-Star every season he played in the 1960s other than 1968—the only year in his career after 1959 in which he failed to hit above .300—and a Gold Glove winner for each of his final 12 seasons, beginning in 1961. He won the NL batting title four times: 1961, 1964, 1965, and 1967, and won the league’s MVP Award in 1966, hitting .317 with 29 home runs and 119 RBIs. In 1967, Clemente registered a career high .357 batting average, hit 23 home runs, and batted in 110 runs. Following that season, in an informal poll conducted by Sport Magazine at baseball’s Winter Meetings, a plurality of major league GMs declared Clemente “the best player in baseball today,” edging out AL Triple Crown winner Carl Yastrzemski by a margin of 8 to 6, with one vote each going to Hank Aaron, Bob Gibson, Bill Freehan and Ron Santo.

Clemente was married on November 14, 1964, to Vera Zabala at San Fernando Church in Carolina. The couple had three children: Roberto Jr., born in 1965, Luis Roberto, born in 1966, and Roberto Enrique, born in 1969. Vera Clemente died on November 16, 2019, aged 78.

The 1970 season was the last one that the Pirates played at Forbes Field before moving to Three Rivers Stadium; for Clemente, abandoning this stadium was an emotional situation. The Pirates’ final game at Forbes Field occurred on June 28, 1970. That day, Clemente noted that it was hard to play in a different field, saying, “I spent half my life there.” The night of July 24, 1970, was declared “Roberto Clemente Night”; on this day, several Puerto Rican fans traveled to Three Rivers Stadium and cheered Clemente while wearing traditional Puerto Rican attire. A ceremony to honor Clemente took place, during which he received a scroll with 300,000 signatures compiled in Puerto Rico, and several thousands of dollars were donated to charity work following Clemente’s request.

During the 1970 season, Clemente compiled a .352 batting average; the Pirates won the NL East pennant but were subsequently eliminated by the Cincinnati Reds. During the offseason, Roberto Clemente experienced some tense situations while he was working as manager of the Senadores and when his father, Melchor Clemente, experienced medical problems and underwent surgery.

In the 1971 season, the Pirates won the NL East, defeated the San Francisco Giants in four games to win the NL pennant, and faced the Baltimore Orioles in the World Series. Baltimore had won 101 games (third season in row with 100+ wins) and swept the American League Championship Series, both for the third consecutive year, and were the defending World Series champions. The Orioles won the first two games in the series, but Pittsburgh won the championship in seven games. This marked the second occasion that Clemente helped win a World Series for the Pirates. Over the course of the series, Clemente had a .414 batting average (12 hits in 29 at-bats), performed well defensively, and hit a solo home run in the deciding 2–1 seventh game victory. Following the conclusion of the season, he received the World Series Most Valuable Player Award.

Since 1971, MLB has presented the Roberto Clemente Award (named the Commissioner’s Award in 1971 and 1972) every year to a player with outstanding baseball playing skills who is personally involved in community work. A trophy and a donation check for a charity of the player’s choice is presented annually at the World Series. A panel of three makes the final determination of the award recipient from an annual list of selected players.

Clemente spent much of his time during the off-season involved in charity work. When Managua, the capital city of Nicaragua, was affected by a massive earthquake on December 23, 1972, Clemente (who visited Managua three weeks before the quake) immediately set to work arranging emergency relief flights. He soon learned, however, that the aid packages on the first three flights had been diverted by corrupt officials of the Somoza government, never reaching victims of the quake. He decided to accompany the fourth relief flight, hoping that his presence would ensure that the aid would be delivered to the survivors. The airplane he chartered for a New Year’s Eve flight, a Douglas DC-7 cargo plane, had a history of mechanical problems and an insufficient number of flight personnel (missing both a flight engineer and copilot), and was overloaded by 4,200 pounds (1,900 kg). It crashed into the Atlantic Ocean off the coast of Isla Verde, Puerto Rico immediately after takeoff on December 31, 1972 due to engine failure.

On March 20, 1973, the Baseball Writers’ Association of America held a special election for the Baseball Hall of Fame. They voted to waive the waiting period for Clemente, due to the circumstances of his death, and posthumously elected him for induction into the Hall of Fame, giving him 393 out of 420 available votes, for 92.7% of the vote.

1973: Olu Clemente — The Philosopher of Baseball, a bilingual play featuring poetry, music and dancing, by Miguel Algarin and Jesús Abraham Laviera, performed on August 30, 1973 at the Delacorte Theatre, Central Park, and published in 1979 in Nuevos pasos: Chicano and Puerto Rican drama by Nicolás Kanellos and Jorge A. Huerta.

Clemente’s Hall of Fame plaque originally had his name as “Roberto Walker Clemente” instead of the proper Spanish format “Roberto Clemente Walker”; the plaque was recast in 2000 to correct the error.

In an interview for the ESPN documentary series SportsCentury in 2002, Clemente’s widow Vera mentioned that Clemente had told her several times that he thought he was going to die young. Indeed, while being asked by broadcaster and future fellow Hall of Famer Richie Ashburn in July 1971 during the All-Star Game activities about when he would get his 3,000th career hit, Clemente’s response was “Well, uh, you never know. I, I, uh, if I’m alive, like I said before, you never know because God tells you how long you’re going to be here. So you never know what can happen tomorrow.” Clemente’s older stepbrother, Luis, died on December 31, 1954 and his stepsister a few years later.

In the 1958–59 off-season, Clemente enlisted in the United States Marine Corps, and served during off-seasons through 1964. He was inducted into the Marine Corps Sports Hall of Fame in 2003, and into the Puerto Rican Veterans Hall of Fame 15 years later.

2008: “Roberto Clemente”: One-hour biography as part of the Public Broadcasting Service history series, American Experience which premiered on April 21, 2008. The film is directed by Bernardo Ruiz, narrated by Jimmy Smits and features interviews with Vera Clemente, Orlando Cepeda and George F. Will. The production received an ALMA Award.

2011: DC-7: The Roberto Clemente Story, a bilingual musical about Clemente’s life, had its world premiere in November 2011 with a full house at the Teatro SEA in Manhattan before moving to New York’s Puerto Rican Traveling Theatre for a successful seven-week run. The show ran from December 6 through December 16, 2012 at Puerto Rico’s Teatro Francisco Arrivi.

In July 2017, Rossi claimed that the canonization requirement of a miracle was met that month when Jamie Nieto, who played Clemente in Rossi’s film and was paralyzed from the neck down in a backflip accident three years after the Clemente film was released, walked 130 steps at his own wedding to fellow Olympian Shevon Stoddart, though Nieto himself stated that the success was due to his hard work, while the Vatican stated that they were not in continued contact with Rossi.