As a senior and captain of the team, Workman had a 10–2 win–loss record with a 0.81 earned run average (ERA) and 171 strikeouts in 76 innings.

In 2012, Workman was named the Red Sox's 2012 Minor League Pitcher of the Year, after pitching 20 games (all starts) for the Salem Red Sox and leading the Class A-Advanced Carolina League in fewest baserunners per nine innings, while ranking second in walks plus hits per inning pitched (WHIP) and fourth in ERA.

He was promoted to the Portland Sea Dogs of the Class AA Eastern League where he appeared in five games (all starts) and had a 3–1 record and 3.96 ERA.

He was promoted to the Pawtucket Red Sox of the Class AAA International League, where he would appear in six games (all starts) with a 3–1 record and 2.80 ERA.

In his major league debut against the Seattle Mariners on July 10, Workman pitched two innings in relief, gave up three runs, and struck out four.

He pitched a perfect 8th inning in the decisive Game 6 of the 2013 World Series, setting up Boston closer Koji Uehara.

[7] On May 30, 2014, Workman was ejected from a game at Fenway Park after throwing a high pitch behind Evan Longoria of the Tampa Bay Rays.

[15] He was optioned to Triple-A Pawtucket to start the 2017 season; he would make 18 relief appearances with the PawSox, with a 1.55 ERA and 1.000 WHIP.

[21] Workman was optioned to Triple-A Pawtucket prior to the start of the 2018 Boston Red Sox season, following limited success during spring training (9 appearances, 5.59 ERA, 1.76 WHIP).

[24] Workman was recalled to Boston from July 31 until August 12,[24][25] when Chris Sale was on the disabled list, making five relief appearances and allowing one run in 5+2⁄3 innings (1.59 ERA).

[26] Workman was on Boston's postseason Roster for the ALDS and ALCS, making three relief appearances and allowing a combined five runs in one inning pitched.

[26] He was replaced on the roster by Pomeranz for the World Series,[27] which the Red Sox went on to win over the Los Angeles Dodgers.

[26] He finished the 2019 season as Boston’s closer, and was named AL Reliever of the Month for September when he pitched 11+1⁄3 innings without allowing an earned run and converted all seven save opportunities.

[26] On August 21, 2020, Workman was traded to the Philadelphia Phillies along with Heath Hembree and cash for Nick Pivetta and Connor Seabold.

[42] Workman made his 2021 Red Sox debut later that day; in closing out a 5–1 win against the Houston Astros, he allowed a home run by Yuli Gurriel.

[45] Overall in his second stint with the Red Sox, Workman made 19 relief appearances, pitching to a 1–0 record with 4.95 ERA while striking out 14 batters in 20 innings.