Marcus Walter Walden[1] (born September 13, 1988) is an American professional baseball pitcher who is a free agent.

[10] He made one start for the Pensacola Blue Wahoos of the Double–A Southern League, allowing 5 runs (4 earned) in 3 innings.

[13] He split time between the Double–A Chattanooga Lookouts and Triple–A Rochester Red Wings, appearing in a combined 42 games with a 2.40 ERA and 1.065 WHIP with six saves and 40 strikeouts in 56+1⁄3 innings pitched.

After pitching effectively during spring training, Walden was named to the Opening Day 25-man roster for the 2018 Boston Red Sox, expected to be the long reliever for rookie manager Alex Cora.

[16][17] Walden made his major league debut on April 1, pitching 1+1⁄3 innings of relief against the Tampa Bay Rays, giving up no runs and one hit while facing five batters.

[19] 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.

[27] Overall with the 2020 Red Sox, Walden appeared in 15 games, all in relief, compiling an 0–2 record with 9.45 ERA and 10 strikeouts in 13+1⁄3 innings pitched.

[28] On February 24, 2021, Walden was designated for assignment by the Red Sox after the signing of Marwin González was made official.

[32] On April 20, 2022, Walden signed with the Gastonia Honey Hunters of the Atlantic League of Professional Baseball.

He made 16 appearances (9 starts) for the Triple-A Nashville Sounds, logging an 0–3 record and 4.53 ERA with 52 strikeouts in 59.2 innings pitched.