Helsley attended Sequoyah High School in Tahlequah, Oklahoma, where he played baseball, basketball, and football along with running track. Undrafted out of high school in the 2013 MLB draft, he enrolled at Northeastern State University where he played college baseball. In 2014, as a freshman, he went 7–4 with a 4.60 ERA in 14 games and was named the MIAA Freshman of the Year. As a sophomore, he pitched to a 14–8 record and 4.06 ERA in innings pitched. After his sophomore season, he was drafted by the St. Louis Cardinals in the fifth round of the 2015 MLB draft and he signed. After signing, Helsley made his professional debut with the Johnson City Cardinals and spent all of 2015 there, posting a 2.01 ERA in innings. In 2016, he pitched for the Peoria Chiefs, where he posted a 10–2 record with a 1.61 ERA in 17 starts and was named a Midwest League All-Star. Helsley started 2017 with the Palm Beach Cardinals and after going 8–2 with a 2.69 ERA in 17 games, he was promoted to the Springfield Cardinals in July. In six starts for Springfield, he was 3–1 with a 2.67 ERA. He also made one start for the Memphis Redbirds at the end of the season. Following the season, he was named the Florida State League Pitcher of the Year. Helsley began 2018 with Springfield and was promoted to Memphis during the season. However, shoulder fatigue ended his season in June. In seven starts for Springfield he was 3–2 with a 4.39 ERA, and in five starts for Memphis he pitched to a 2–1 record and a 3.71 ERA. The Cardinals added Helsley to their 40-man roster after the 2018 season. Helsley began 2019 back with Memphis. On April 16, he was recalled to the major leagues for the first time. He made his debut that night, throwing two and a third innings in relief and recording a single in his first major leagueat bat. Helsley was placed on the injured list on June 13 with right shoulder impingement, and was reassigned to Memphis following his activation on July 3. Helsley was recalled for the final time on August 4, spending the remainder of his 2019 regular season in St. Louis' bullpen. Over relief innings with the Cardinals, Helsley went 2–0 with a 2.95 ERA, striking out 32. In that year's postseason, Helsley pitched innings with no earned runs and 8 strikeouts.
