Riley O’Brien Bio
Riley Chun-Young O’Brien is an American professional baseball pitcher for the St. Louis Cardinals of Major League Baseball (MLB). He has previously played in MLB for the Cincinnati Reds and Seattle Mariners and made his MLB debut in 2021. A right-handed pitcher with a background in starting, O’Brien has also developed into a relief role in recent seasons.
Drafted by the Tampa Bay Rays in 2017, O’Brien worked his way through the minor leagues before reaching the majors. He comes from a family with deep baseball roots, as his grandfather and great uncle both played in the major leagues.
Early Life and Background
Riley Chun-Young O’Brien was born on February 6, 1995. He is of Korean descent on his mother’s side. O’Brien grew up in the Pacific Northwest and attended Shorewood High School in Shoreline, Washington, where he played baseball. He graduated from Shorewood in 2013.
After high school, O’Brien enrolled at Everett Community College and spent two seasons there. He later transferred to the College of Idaho to continue his development as a pitcher. As a junior in 2016, he went 6–3 with a 3.23 earned run average (ERA) and 60 strikeouts over 69 innings pitched for the Coyotes. In his senior year of 2017, he posted a 3–4 record and a 2.15 ERA over 67 innings.
Path to Baseball
Following his senior season at the College of Idaho, the Tampa Bay Rays selected O’Brien in the eighth round of the 2017 Major League Baseball draft. He signed with the organization and began his professional career that same year. O’Brien’s path through the minors was steady, as he moved from short-season ball to full-season affiliates over the next several seasons.
His progression through the Rays system was marked by strong early performances. He earned Appalachian League Pitcher of the Week honors twice in his first professional season and was later named a Midwest League All-Star. These accomplishments helped establish him as a promising arm in the organization before he was traded to the Cincinnati Reds in August 2020.
Riley O’Brien Career
Early Career (2017–2020)
O’Brien made his professional debut in 2017 with the Princeton Rays of the Advanced Rookie Appalachian League, going 1–0 with a 2.20 ERA over 11 games, including ten starts. In 2018, he split the season between the Bowling Green Hot Rods of the Single-A Midwest League and the Charlotte Stone Crabs of the High-A Florida State League, combining to go 8–4 with a 2.75 ERA over 25 games and 13 starts.
In 2019, O’Brien began the year with Charlotte before a May promotion to the Montgomery Biscuits of the Double-A Southern League. Over 20 games and 17 starts, he posted a 7–6 record and a 3.16 ERA. He did not play in 2020 due to the cancellation of the minor league season caused by the COVID-19 pandemic.
Tampa Bay Rays Era (2017–2020)
O’Brien began his professional career in the Tampa Bay Rays organization after being drafted in the eighth round of the 2017 MLB draft. He was named Appalachian League Pitcher of the Week twice during his debut season with the Princeton Rays, signaling his early potential. The Rays system gave him consistent opportunities to develop as a starting pitcher.
In 2018, O’Brien was named a Midwest League All-Star with Bowling Green before finishing the year with Charlotte. His 2019 campaign saw him reach Double-A Montgomery. On August 28, 2020, the Rays traded O’Brien to the Cincinnati Reds in exchange for Cody Reed, ending his time in the Tampa Bay system.
Cincinnati Reds Era (2020–2022)
On November 20, 2020, the Reds added O’Brien to their 40-man roster to protect him from the Rule 5 draft. He began the 2021 season with the Triple-A Louisville Bats, where he posted a 7–7 record and a 4.55 ERA with 121 strikeouts over 112⅔ innings across 23 games and 22 starts. On September 28, 2021, the Reds recalled O’Brien to the active roster for his MLB debut against the Chicago White Sox. He started the game and threw 1⅓ innings, allowing two solo home runs while walking three and striking out two.
On April 13, 2022, the Reds designated O’Brien for assignment to make room for pitcher Nick Lodolo, ending his time in the Cincinnati organization. He appeared in only one major league game for the Reds during his tenure.
Seattle Mariners Era (2022–2023)
On April 16, 2022, the Reds traded O’Brien to the Seattle Mariners for cash considerations or a player to be named later. He was designated for assignment on May 27 and later cleared waivers, being sent outright to the Triple-A Tacoma Rainiers on June 2. O’Brien spent the rest of the 2022 season in the minors.
O’Brien spent the entirety of the 2023 season at the Triple-A level with Tacoma. In 51 appearances, he registered a 2.29 ERA with 86 strikeouts and 15 saves across 55.0 innings of work, showing growth as a reliever.
St. Louis Cardinals Era (2023–Present)
On November 5, 2023, O’Brien was traded to the St. Louis Cardinals and added to the 40-man roster. The Cardinals officially revealed on March 26, 2024, that O’Brien had made the Opening Day roster, but a flexor strain led to an injured list placement on March 31, and he was later transferred to the 60-day injured list on May 6. O’Brien was activated on August 11 and made 8 total appearances for St. Louis, posting an 11.25 ERA with 11 strikeouts over 8 innings.
Heading into 2025, O’Brien was optioned to the Triple-A Memphis Redbirds. On August 4, 2025, O’Brien recorded his first career win against the Los Angeles Dodgers. Two days later, he recorded his first career save, marking a significant breakthrough in his major league career.
Driving Style and Strengths
O’Brien has shown adaptability throughout his career, transitioning from a starting pitcher role in the minor leagues to a relief role at the major league level. His minor league track record with Tacoma, where he recorded a 2.29 ERA and 15 saves in 2023, suggests strong performance in high-leverage situations. His ability to strike out batters at a consistent rate has been a hallmark of his development.
Notable Events and Milestones
One of the defining moments of O’Brien’s career came on August 4, 2025, when he earned his first career MLB win against the Los Angeles Dodgers. Two days later, he added his first career save, both coming during his time with the St. Louis Cardinals. His MLB debut on September 28, 2021, against the Chicago White Sox also stands as a key career milestone.
Riley O’Brien Career Wins
Riley Chun-Young O’Brien has compiled a professional career that includes work as both a starting pitcher and a reliever. His first career MLB win came on August 4, 2025, while pitching for the St. Louis Cardinals, followed by his first career save two days later. Across the minor leagues, O’Brien posted consistent results, including an 8–4 record in 2018 and a 7–6 mark in 2019.
MLB Highlights
O’Brien made his MLB debut on September 28, 2021, as a starting pitcher for the Cincinnati Reds against the Chicago White Sox. He appeared in games for the Reds, Mariners, and Cardinals before earning his first career decisions with St. Louis in August 2025. His first win and first save both came in the same week, signaling a major step forward in his major league career.
Other Wins & Performances
During his time in the minor leagues, O’Brien earned Appalachian League Pitcher of the Week honors twice in 2017 and was named a Midwest League All-Star in 2018. His 2023 season at Triple-A Tacoma featured a 2.29 ERA and 15 saves across 51 appearances, showcasing his effectiveness in a relief role.
Riley O’Brien Family
Family Background and Racing Lineage
O’Brien comes from a family with a strong baseball tradition. His grandfather, Johnny O’Brien, played six seasons in the major leagues. His great uncle, Eddie O’Brien, also played in the majors, giving Riley a notable baseball lineage that has shaped his path in the sport.
Personal Life
Riley O’Brien is married to Chellyn O’Brien. The couple had their wedding in late 2023. O’Brien is of Korean descent on his mother’s side, adding to his diverse family heritage.
2025 Season Performance
The 2025 season has been a breakthrough year for Riley Chun-Young O’Brien. He began the year with the Triple-A Memphis Redbirds after being optioned by the St. Louis Cardinals. His strong performance in the minors led to a return to the major league roster, where he made an immediate impact.
On August 4, 2025, O’Brien recorded his first career MLB win against the Los Angeles Dodgers, followed by his first career save two days later. These milestones marked a turning point in his career, validating his transition from starting pitcher to reliever.
With the Cardinals in the thick of their season, O’Brien’s emergence as a reliable bullpen arm has been a key storyline. His ability to perform in high-pressure situations has positioned him as a potential late-inning option for St. Louis moving forward.