The Oakland Athletics drafted Beck as a starting pitcher in the 13th round (327th pick) of the 1986 Major League Baseball Draft. Prior to the 1988 season, he was traded to the San Francisco Giants organization. In 1989, while with the San Jose Giants of the California League, he posted a record of 11–2 between opening day and June 14, when he was promoted to the Shreveport Captains of the Double A Texas League.

Beck made his Major League debut on May 6, 1991, against the Montreal Expos. His performance was forgettable (2.0 IP, 3 H, 2 ER), but his season numbers were more impressive. He had a 3.78 ERA, pitched 52 ⁄3 innings in 31 games, and struck out 38 while walking 13. In 1992, Beck took over as the regular closer from Dave Righetti and posted a record of 3–3 with 17 saves and a 1.76 ERA. He pitched 92 innings over 65 games and struck out 87 while walking only 15. In 1993 he recorded 48 saves, including 24 consecutive. At the time, both marks were Giants franchise records. Beck found success using a sinker, slider, and splitter.

After the 1997 season, the Giants felt Beck’s best years were behind him, and allowed him to leave as a free agent to sign with the Chicago Cubs, replacing him with Robb Nen. Beck set a career high in saves in 1998, his first season with the Cubs, converting 51 of 58 chances. However, in the 1999 season, Beck battled injury, and was traded by Chicago to the Boston Red Sox in exchange for reliever Mark Guthrie and a player to be named later, who turned out to be Cole Liniak.

In 2003, Beck returned to the Major Leagues with the Padres, filling in for the injured Trevor Hoffman. He converted 20 saves in 20 chances, while posting a 1.78 ERA. His statistics earned him the National League Comeback Player of the Year award. In 2004, Beck dealt with personal problems during Spring Training and struggled in a seventh inning role for the Padres. Beck was released by San Diego in August.

On June 23, 2007, Beck died alone at his home in Phoenix, Arizona. The Maricopa County medical examiner has not publicly disclosed the cause of death and the Phoenix police did not suspect foul play. Beck’s ex-wife stated she believed Beck’s death to be drug related. Cocaine and heroin were found in his home and bedroom.