Donaldson was raised by his mother, Lisa French, while his father, Levon Donaldson, was imprisoned for most of Josh’s childhood. His father, a construction worker, was sentenced in 1992 on charges of sexual battery, false imprisonment, and aggravated battery, and released from prison in 2007.

Donaldson later attended Auburn University, where he played college baseball as a catcher and third baseman for the Auburn Tigers baseball team in the Southeastern Conference. During his freshman season in 2005, Donaldson started 39 games at third base, hitting .294 with seven home runs, and also began learning to play catcher. In his sophomore season, Donaldson hit .276 and led the team with ten home runs; he also threw out 15 of 38 base stealers and had seven pickoffs. In the summer of 2006, Donaldson played for the Harwich Mariners of the Cape Cod Baseball League where he was an All-Star and hit .302. In 2007, Donaldson was named a Louisville Slugger Preseason All-American.

The Chicago Cubs drafted Donaldson as a catcher in the first round (48th overall) of the 2007 Major League Baseball draft. In his first minor league season Donaldson played 53 games for the Rookie Arizona League Cubs and Short Season-A Boise Hawks, batting a combined .335 with nine home runs and 25 RBIs. He also walked more than he struck out, with 39 and 38 respectively. In 2008, he played 63 games with the Class-A Peoria Chiefs, where he hit .217 with six home runs and 23 RBIs. Donaldson was then traded, along with Matt Murton, Eric Patterson and Sean Gallagher, to the Oakland Athletics for Rich Harden and Chad Gaudin. He played 47 games with the Advanced-A Stockton Ports, where he batted .330 and had nine home runs and 39 RBIs. Donaldson then played the entire 2009 season with the Double-A Midland RockHounds, and recorded a batting average of .270 with nine home runs and 91 RBIs.

Donaldson was called up to the majors for the first time on April 30, 2010, filling in for injured catcher Kurt Suzuki. He made his debut that night as a pinch hitter, and struck out. The next day, he recorded his first major league hit, a two-run home run on the first pitch by Toronto Blue Jays pitcher Dana Eveland. In 14 games played during the 2010 season, Donaldson made 34 plate appearances and recorded five hits. After returning to the minor leagues, he spent the season with the Triple-A Sacramento River Cats and hit .238 with 18 home runs and 67 RBIs for the season. Donaldson played the entire 2011 season in Sacramento, improving his average to .261, and hit 17 home runs and 70 RBIs.

Against Detroit Tigers reliever Brayan Villarreal, Donaldson hit his first career walk-off home run on April 12, 2013. It was the A’s first walk-off win in 2013. He hit his first career grand slam on June 7 against Chicago White Sox starter Chris Sale. Major League Baseball named Donaldson the American League Player of the Month for September after batting .337 with 20 runs scored, eight doubles, five home runs and 16 RBIs in 25 games. He played 158 games and finished the season with 24 home runs, 93 RBIs and a .301 average and placed fourth in AL MVP voting.

His father watched him play baseball in person for the first time on September 13, 2013, against the Texas Rangers in Arlington, Texas. Donaldson walked twice and hit a home run as well as a double in three at-bats as the Athletics won, 9–8.

Donaldson was elected to his first All-Star appearance in 2014 as the starter at third base for the American League. Donaldson hit a three-run walk-off home run in the ninth inning against the Baltimore Orioles on July 17 to lead the A’s to a 5–4 victory. Donaldson won his first career Fielding Bible Award for his work at third base. During the 2014 season, Donaldson hit 98 RBIs, 29 home runs, and 93 runs scored, beating out his career highs with Oakland. However, Donaldson’s batting average went down to .255. Donaldson would end up finishing 8th in the AL MVP voting.

On November 28, 2014, the Athletics traded Donaldson to the Toronto Blue Jays for Brett Lawrie, Kendall Graveman, Sean Nolin, and Franklin Barreto. The following February, he lost his salary arbitration case against the Blue Jays after seeking $5.75 million. Instead, he was awarded the Blue Jays’ offer of $4.3 million for the 2015 season.

By the end of August, observers began referring to Donaldson’s season as one of the best in Blue Jays’ history. Several members of the media wrote articles naming him as the American League Most Valuable Player Award frontrunner over Mike Trout, and fans attending both home and away games began chanting “M-V-P! M-V-P!” when he would bat. On September 7, Donaldson hit his 100th career home run. He hit his 40th home run of the season on September 25, and in doing so, joined Shawn Green and Carlos Delgado as the only players in franchise history to have 40 doubles and 40 home runs in the same season. Donaldson finished the 2015 regular season with a .297 batting average, 122 runs scored, 41 doubles, 41 home runs, and 123 RBIs. According to Baseball-Reference.com, his 8.8 Wins Above Replacement (WAR) in 2015 ranked as the highest single-season total in club history, surpassing José Bautista’s previous record of 8.1 in 2011.

Sporting News announced on October 29, 2015, that Donaldson had won their MLB Player of the Year Award. Other awards included the American League Hank Aaron Award, the American League third baseman’s Silver Slugger Award, and Players Choice Awards for both Major League Player of the Year and American League Outstanding Player. On November 19, 2015, Donaldson was named the 2015 American League Most Valuable Player (AL MVP), finishing ahead of Mike Trout and Lorenzo Cain. On December 5, 2015, Donaldson was revealed as the cover athlete for MLB The Show 16.

In February 2016, Donaldson and the Blue Jays appeared to be heading to salary arbitration for the second consecutive year. Donaldson had asked for $11.8 million for the 2016 season, while the Blue Jays had countered at $11.35 million. On February 10, Donaldson signed a two-year, $28.65 million extension that paid him $11.65 million in 2016 and $17 million in 2017.

In the first half of 2016, Donaldson resumed the high level of play from his MVP season. He won the June 19 Player of the Week Award after hitting three home runs, four doubles, one triple and nine runs driven in with 12 hits in 27 at bats. He led the league in total bases (27), extra-base hits (8) and tied for first in slugging percentage (1.000). On July 7, he was announced as a reserve for the American League in the 2016 All-Star Game. Heading into the All-Star break, Donaldson was batting .304 with 23 home runs and 63 RBIs. He had also scored 80 runs, which made him the first player in Blue Jays history to do so before the All-Star break. On August 28, Donaldson hit three home runs in a game for the first time in his career, leading the Blue Jays to a 9–6 win and a sweep of the Minnesota Twins. Donaldson finished the 2016 regular season with a .284 batting average, 37 home runs, and 99 RBI.

Donaldson is a fan of the History channel series Vikings, and in January 2016, it was announced that he would have a guest appearance in the fourth season of the show as “Hoskuld”. Donaldson took his nickname, “Bringer of Rain”, from the Starz TV series Spartacus: Blood and Sand.

On April 13, 2017, Donaldson left the game after straining his right calf, and was placed on the 10-day disabled list the following day. He returned to the lineup in late May. From August 1 to the end of the 2017 season, Donaldson hit .302 with 22 home runs in 227 plate appearances.

On January 12, 2018, Donaldson avoided salary arbitration with the Blue Jays by agreeing to a one-year, $23 million contract for the 2018 season.

On August 31, 2018, the Blue Jays traded Donaldson to the Cleveland Indians for a player to be named later, later revealed to be pitching prospect Julian Merryweather. Donaldson wore the number 27 as number 20 is retired in honor of Frank Robinson. On September 3, he was placed on the 10-day disabled list due to a left calf strain, and sent to the Triple-A Columbus Clippers on a rehab assignment, where he hit a grand slam in his first rehab game. The Indians activated Donaldson from the disabled list on September 11, 2018. Donaldson made his Indians debut that evening, starting at third base and batting fifth.

On November 26, 2018, Donaldson signed a 1-year, $23 million contract with the Atlanta Braves.

In 2019 he batted .259/.379/.521 with 37 home runs and 94 RBIs. He made contact with the lowest percentage of pitches he swung at in the strike zone (76.6%) of all NL batters. On defense in 2019, he had a 15 Defensive Runs Saved (DRS) rating, the best in the National League among third basemen. He was named the 2019 NL Comeback Player of the Year.

On January 22, 2020, Donaldson signed a four-year $92 million contract with the Minnesota Twins.