Helsley attended Sequoyah High School in Tahlequah, Oklahoma,[1] where he played baseball, basketball, and football along with running track.

[2] Undrafted out of high school in the 2013 MLB draft, he enrolled at Northeastern State University where he played college baseball.

[6][5] After signing, Helsley made his professional debut with the Johnson City Cardinals and spent all of 2015 there, posting a 2.01 ERA in 40+1⁄3 innings.

Helsley was recalled for the final time on August 4, spending the remainder of his 2019 regular season in St. Louis' bullpen.

[23] In 2021, Helsley appeared in 51 games with the Cardinals in which he went 6-4 with a 4.56 ERA and 47 strikeouts over 47+1⁄3 innings before he was shut down in mid-August with knee and elbow injures.

[24] In 2022, Helsley compiled a first-half 5–1 record with a 0.73 ERA, 54 strikeouts, and seven saves over 37 innings, and was consequently selected to represent the Cardinals at the All-Star Game in Los Angeles.

[27] In the post-season, Helsley, who had jammed fingers on his throwing hand in his final regular-season appearance, was the loser in Game 1 of the 2022 National League Wild Card Series, allowing a single, two walks, and a hit batter in successive 9th-inning plate appearances for four earned runs in a game the Philadelphia Phillies won 6-3.

[28] Helsley began the 2023 season in St. Louis' bullpen, and logged a 3.24 ERA in 22 appearances before he was placed on the injured list with a right forearm strain on June 12, 2023.

He was named NL Reliever of the Month for April 2024, with his 16 appearances, 10 saves, a 1.69 ERA, and 9.5-to-1 strikeout-to-walk ratio (19 strikeouts, 2 walks).