[1] He had agreed to terms to sign with the Colorado Rockies, but a Yankees scout matched their offer and convinced Severino to play for the team he had grown up as a fan of.

[1] Combined between the three teams, Severino went 6–5 win–loss record with a 2.46 ERA, 127 strikeouts, and 27 walks in 24 games (all starts) and 113 innings pitched.

[6] Before the start of the 2015 season, Severino was ranked the best prospect in the Yankees farm system and the 23rd best out of all minor league players by MLB Pipeline.

[7] Severino began the 2015 season with Trenton, where he had a 2–2 win–loss record with a 3.32 ERA and 48 strikeouts in 38 innings pitched across eight games started.

[8] Yankees' manager Joe Girardi set Severino's major league debut for August 5.

[15] Additionally, he became the first AL pitcher in MLB history to strike out seven hitters while walking none and allowing no more than two hits in their major league debut.

[21] On September 26, Severino was ejected for the first time in his Major League career after hitting Justin Smoak with a pitch.

On April 13, 2017, Severino struck out a career-high 11 batters in seven innings as the Yankees won 3–2 over the Tampa Bay Rays.

[24] In a no-decision, he struck out a career-high 12 batters in seven innings against the White Sox on June 27 as the bullpen blew a lead for the sixth time in Severino's starts.

[24] He finished his first half on a high note though, striking out 10 batters over seven innings of three-run ball against the Milwaukee Brewers on July 8, his fourth start of the season with at least 10 strikeouts.

Severino was named to the American League All-Star team alongside his teammates Aaron Judge, Gary Sanchez, Starlin Castro and Dellin Betances.

Severino started the second half strong, first matching Chris Sale by allowing one run over seven innings in a pitcher's duel against the Red Sox.

[27] As of July 27, Severino was tied with Max Scherzer for second-most starts (8) of at least seven innings pitched with one earned run or less in the 2017 season, behind Clayton Kershaw's 11.

His 16 starts of one run allowed or less led the major leagues, additionally he was the first Yankee starter to have 16 starts with one or no runs allowed in a single season since Mike Mussina in 2001 and the youngest pitcher in the major leagues to reach this mark since Dwight Gooden in 1985.

[32] He went on to finish the 2017 postseason with a 1–1 record and a 5.68 ERA in 16 innings (4 starts) as the Yankees lost to the Houston Astros in seven games in the American League Championship Series.

On July 1, Severino became the first Yankee since CC Sabathia in 2011 to win 13 games prior to the All-Star break after throwing 6+2⁄3 shutout innings to beat the Red Sox.

Owning a 14–2 record and a 2.12 ERA, Severino was named to the 2018 Major League Baseball All-Star Game, his second consecutive selection.

[36] He finished the first half of the season 14–2 with a 2.31 ERA in 20 starts, with 144 strikeouts against 32 walks in 128+1⁄3 innings and posting a .209 opponent batting average and 1.01 WHIP.

[37] For the second consecutive year, he led all major league pitchers with an average fastball velocity of 97.6 miles per hour.

[43] On February 25, 2020, it was announced that Severino would undergo Tommy John surgery to repair a partially torn ulnar collateral ligament in his right elbow, ending his 2020 season.

On June 12, 2021, Severino suffered a groin injury during a rehab start with the Hudson Valley Renegades and was sidelined until August.

The potential combined no-hitter was broken up in the eighth inning when Josh Jung recorded a hit off Yankees reliever Miguel Castro.

[51] On September 9, 2023, manager Aaron Boone announced that Severino's season was over after he suffered a high–grade oblique strain in the Yankees' loss against the Milwaukee Brewers the previous day.

[59] With a three-quarters delivery, Severino currently throws four pitches: a four-seam fastball averaging 98 mph,[57] a slider, a change-up and as of 2022, a cutter.