On 18 December 2014, aged 18, Sepúlveda was signed by the Chicago Cubs organization as an international free agent.[4]
In 2015, Sepúlveda made his professional debut with the rookie-level Arizona Complex League Cubs, hitting .281/.351/.308 with 25 RBI. The next year, he played for the South Bend Cubs of the Single-A Midwest League, appearing in 80 games, batting .310/.366/.374 with one home run and 24 RBI. In 2017, Sepúlveda played for the Myrtle Beach Pelicans of the High-A Carolina League, hitting .196/.272/.214 and seven RBI in 28 games; he also appeared in nine games with the AZL Cubs.[5]
In 2019, Sepúlveda made 112 appearances for Myrtle Beach, hitting .243/.342/.285 with 36 RBI and 14 stolen bases.[5]
On 12 December 2019, the Los Angeles Dodgers selected Sepúlveda from the Cubs in the Rule 5 draft, and assigned him to the Triple-A Oklahoma City Dodgers.[6][7] He did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[8] Sepúlveda was released by the Dodgers on 22 March 2021, without having appeared in a single game for the organization.[4]
On 7 June 2021, Sepúlveda signed a minor league contract to return to the Chicago Cubs organization, who subsequently assigned him to the Tennessee Smokies of the Double-A Southern League. He made 73 appearances for the Smokies, batting .213/.318/.293 with three home runs and 21 RBI. In 2022, Sepúlveda played for the Iowa Cubs of the Triple-A International League, appearing in 24 games and hitting .245/.349/.283 with nine RBI and one stolen base.[5] He elected free agency following the season on 10 November 2022.[4]
On 3 February 2023, Sepúlveda joined the Diablos Rojos del México of the Mexican League (LMB).[2][3] He made his LMB debut on 21 April appearing as a pinch hitter against the Tigres de Quintana Roo in the Estadio Alfredo Harp Helú.[9] In 2023, Sepúlveda appeared in 73 contests for the Diablos, hitting .314/.411/.400 with three home runs, 37 RBI, and two stolen bases.
Sepúlveda made 58 appearances for the team during the 2024 season, slashing .340/.442/.431 with one home run, 31 RBI, and six stolen bases. Sepúlveda made 69 appearances for México in 2025, batting .395/.503/.515 with two home runs, 38 RBI, and 12 stolen bases. With the team, he won his second consecutive Serie del Rey.[10]
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