The Toronto Blue Jays selected Walden in the ninth round of the 2007 MLB draft. in 2011 After pitching with Toronto's Rookie League and Class A Short-Season teams during 2007 and 2008, Walden missed most of the 2009 season and the entire 2010 season due to shoulder and elbow injuries that required surgeries, including Tommy John surgery. He returned to pitch for several Toronto farm teams during the 2011 through 2014 seasons, ultimately being promoted to the Triple-ABuffalo Bisons. The Blue Jays promoted Walden to the major leagues in April 2014, but they optioned him back to the minor leagues five days later without using him in a major league game. Six days later, the Blue Jaysdesignated Walden for assignment.
Walden signed with the Minnesota Twins organization for the 2016 season. He split time between their Double-A and Triple-A affiliates, appearing in a combined 42 games with a 2.40 ERA and 1.065 WHIP with six saves and 40 strikeouts in innings pitched.
Boston Red Sox
In December 2016, Walden signed with the Boston Red Sox. He pitched for the Triple-A Pawtucket Red Sox during the 2017 season, pitching innings in 29 games with a 10–6 record, 3.92 ERA, and 1.306 WHIP while recording 86 strikeouts and 36 walks. After pitching effectively during spring training, Walden was named to the Opening Day25-man roster for the 2018 Boston Red Sox, expected to be the long reliever for rookie manager Alex Cora. Walden made his major league debut on April 1, pitching innings of relief against the Tampa Bay Rays, giving up no runs and one hit while facing five batters. On April 14, he earned his first save, pitching three innings of relief in a 10–3 win over the Baltimore Orioles.. He was sent down to the Triple-A Pawtucket Red Sox before the end of the month, was recalled very briefly in early May, and then spent the remainder of the season in the minors. With Boston, he appeared in a total of eight games with a 0–0 record and one save, while recording a 3.68 ERA and 14 strikeouts in innings. In 2019, Walden was optioned to Triple-A Pawtucket prior to Opening Day. He was called up on April 6, when Brian Johnson was placed on the injured list, and recorded his first MLB win the next day, pitching two innings of scoreless relief in a 1–0 win over the Arizona Diamondbacks. He was optioned back to Pawtucket effective on April 16, then recalled to Boston on April 19. Overall with the 2019 Red Sox, Walden appeared in 70 games, compiling a 9–2 record with 3.81 ERA and 76 strikeouts in 78 innings.
Personal life
Walden and his wife, Nichole, have two daughters, Sutton and Palmer. Walden and two business partners opened the DIB Baseball Academy in Fresno in 2015.
