Riley Chun-Young O’Brien Bio
Riley Chun-Young O’Brien (born February 6, 1995) is an American professional baseball pitcher for the St. Louis Cardinals of Major League Baseball. O’Brien made his major league debut in 2021 after a multi-year minor-league development path and has appeared in MLB for the Cincinnati Reds and the Seattle Mariners.
Early Life and Background
Riley O’Brien attended Shorewood High School in Shoreline, Washington, where he played high school baseball and graduated in 2013. After high school he enrolled at Everett Community College and spent two seasons there before transferring to the College of Idaho to continue both his academic and baseball development.
At the College of Idaho O’Brien strengthened his profile as a starting pitcher. As a junior in 2016 he posted a 6–3 record with a 3.23 earned run average and 60 strikeouts across 69 innings. In his senior season in 2017 he produced a 2.15 ERA over 67 innings, performances that helped him draw attention from professional scouts.
Path to Baseball
O’Brien was selected by the Tampa Bay Rays in the eighth round of the 2017 Major League Baseball draft, launching his professional career in the Rays organization. He made his pro debut with the Princeton Rays in the Advanced Rookie Appalachian League in 2017 and earned recognition including Appalachian League Pitcher of the Week twice during that season.
Across 2018 and 2019 O’Brien advanced through the Rays’ minor-league system, starting the 2018 season with the Bowling Green Hot Rods in Single-A where he was named a league All-Star and finishing with the Charlotte Stone Crabs in High-A. By 2019 he reached Double-A with the Montgomery Biscuits, compiling a combined 7–6 record and a 3.16 ERA between levels that year.
Riley Chun-Young O’Brien Career
Early Career (2017–2020)
After the 2017 draft O’Brien progressed steadily through Tampa Bay’s minor-league affiliates. He posted strong ERAs and strikeout totals in the lower minors and earned promotions during the 2018 and 2019 seasons. The 2020 minor-league season was canceled due to the COVID-19 pandemic, halting game action for many prospects including O’Brien.
Cincinnati Reds Breakthrough (2020–2021)
On August 28, 2020, O’Brien was traded from the Tampa Bay Rays to the Cincinnati Reds in exchange for Cody Reed. The Reds added him to their 40-man roster on November 20, 2020, to protect him from the Rule 5 draft, and he began 2021 with the Louisville Bats at Triple‑A.
O’Brien made his major league debut on September 28, 2021, when the Cincinnati Reds recalled him to start against the Chicago White Sox. He worked 1⅓ innings in that first appearance, recording two strikeouts and allowing two solo home runs while issuing three walks as he adjusted to big-league hitters.
Seattle Mariners Period (2022–2023)
In April 2022 the Reds designated O’Brien for assignment and on April 16 he was traded to the Seattle Mariners for cash considerations or a player to be named later; Washington State infielder Luis Chevalier later completed the transaction. O’Brien cleared waivers in 2022 and was outrighted to the Triple-A Tacoma Rainiers in June after a designation for assignment.
O’Brien spent the 2023 season with the Tacoma Rainiers at Triple‑A, appearing in 51 games and registering a 2.29 ERA with 86 strikeouts and 15 saves across 55.0 innings. That season re-established him as an effective late-inning pitcher and contributed to his value as a bullpen option at the major-league level.
St. Louis Cardinals Era (2024–Present)
On November 5, 2023, Riley O’Brien was traded to the St. Louis Cardinals and added to their 40‑man roster. He made the Cardinals’ Opening Day roster in March 2024 but was placed on the injured list on March 31 with a flexor strain and later transferred to the 60‑day injured list on May 6 before being activated on August 11, 2024.
Following activation O’Brien appeared in eight games for St. Louis in 2024, allowing runs as he worked back from injury and recording 11 strikeouts in eight innings. He began the 2025 season optioned to the Triple‑A Memphis Redbirds and later registered his first major-league win on August 4, 2025, against the Los Angeles Dodgers and recorded his first career save two days later on August 6.
Pitching Style and Strengths
O’Brien’s professional record shows a pitcher who developed through starting roles in the minors into a late-inning reliever option in Triple‑A and the majors. His 2023 Triple‑A season emphasized strikeout ability and run prevention, and his adaptability between starting and relief assignments has been a defining strength as he has sought consistent major-league opportunities.
Notable Events and Milestones
Key milestones in O’Brien’s career include his selection in the eighth round of the 2017 draft, his major-league debut with the Cincinnati Reds on September 28, 2021, and his first MLB win and save in August 2025 with the St. Louis Cardinals. His return from a 2024 flexor strain and subsequent contributions in 2025 marked important chapters in his professional progression.
Riley Chun-Young O’Brien Career Wins
Through June 28, 2026, Riley O’Brien recorded six major-league wins, holding a 6–5 win–loss record at the MLB level with a 3.69 earned run average and 93 strikeouts in major-league play during that span. His first MLB victory and save were logged in August 2025 after time between Triple‑A and the majors.
MLB Highlights
O’Brien’s MLB highlights include his 2021 debut with Cincinnati and the accumulation of six major-league victories through mid‑2026. His statistical line through June 28, 2026, reflects progress as a big-league pitcher who has moved between starting assignments in the minors and bullpen roles in the majors.
Other Wins & Perfromances
In the minors O’Brien earned Appalachian League Pitcher of the Week honors twice in 2017 and was named a Midwest League All‑Star in 2018. His 2019 promotions to Double‑A and his strong 2023 Triple‑A campaign with 15 saves and a 2.29 ERA are notable performances that sustained his professional trajectory.
Riley Chun-Young O’Brien Family
Family Background and Baseball Lineage
O’Brien comes from a family with major-league ties: his grandfather Johnny O’Brien played six seasons in Major League Baseball and his great uncle Eddie O’Brien also played in the majors. He is of Korean descent on his mother’s side.
Personal Life
Riley O’Brien married his wife, Chellyn O’Brien, on November 18, 2023. Public records list his residence as unknown; further personal details have not been publicly disclosed beyond his marriage and family baseball lineage.
2025 Season Performance
The 2025 season served as a turning point as O’Brien began the year optioned to Triple‑A Memphis before returning to the majors to record his first big‑league win on August 4, 2025, and his first save on August 6, 2025. Those results underscored his role as a depth option for the Cardinals’ bullpen and demonstrated resilience following earlier injuries.
Looking at his path through 2025, O’Brien combined minor‑league consistency with key major‑league moments that reinforced his standing as a versatile pitcher capable of contributing in relief. His ongoing development positions him as a roster option for St. Louis as he pursues further stability at the major-league level.