Riley O’Brien Bio
Riley Chun-Young O’Brien (born February 6, 1995) is an American professional baseball pitcher who currently plays for the St. Louis Cardinals of Major League Baseball. He has also played in MLB for the Cincinnati Reds and Seattle Mariners, and he made his major league debut in 2021. A right-handed pitcher of Korean descent on his mother’s side, O’Brien is also recognized for a notable baseball family, with his grandfather and great uncle both having reached the major leagues.
After being drafted by the Tampa Bay Rays in 2017, O’Brien worked his way through the minor leagues before reaching the big leagues with Cincinnati. Across his career he has appeared as both a starter and a reliever, and he has represented the Korean National Team in international competition, including the 2026 World Baseball Classic.
Early Life and Background
Riley Chun-Young O’Brien was born on February 6, 1995, and grew up in the Pacific Northwest. He attended Shorewood High School in Shoreline, Washington, where he played baseball and developed the foundation that would eventually carry him to the professional ranks. He graduated from Shorewood in 2013.
After high school, O’Brien enrolled at Everett Community College, where he spent two seasons refining his game on the mound. He later transferred to the College of Idaho, joining the Coyotes program for his final two years of college eligibility.
As a junior in 2016, O’Brien went 6–3 with a 3.23 earned run average and 60 strikeouts over 69 innings pitched for the Coyotes. In his senior year of 2017, he produced a 3–4 record and a 2.15 ERA across 67 innings, a performance that helped push his name up draft boards.
Path to Baseball
Following the 2017 college season, the Tampa Bay Rays selected O’Brien in the eighth round of the 2017 Major League Baseball draft. He signed with the organization and quickly reported to his first professional assignment, beginning a steady climb through the Rays’ farm system.
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 appearances, including 10 starts. He was named Appalachian League Pitcher of the Week twice during that debut season, an early signal of his potential on the mound.
In 2018, O’Brien opened the year with the Bowling Green Hot Rods of the Single-A Midwest League, where he earned an All-Star selection before a midseason promotion to the Charlotte Stone Crabs of the High-A Florida State League. Across 25 games and 13 starts that year, he went 8–4 with a 2.75 ERA. In 2019, he returned to Charlotte and was promoted in May to the Montgomery Biscuits of the Double-A Southern League, finishing the season with a 7–6 record and a 3.16 ERA in 20 games and 17 starts.
Riley O’Brien Career
Early Career (2017–2019)
O’Brien’s first three professional seasons were spent entirely within the Tampa Bay Rays organization, moving one level higher each year. His strongest stretch came in 2018, when his All-Star campaign at Bowling Green and subsequent work at Charlotte established him as a legitimate starting pitching prospect in the system.
He did not appear in a game in 2020 because the minor league season was canceled due to the COVID-19 pandemic, but his progress to that point had already drawn attention from other clubs. On August 28, 2020, the Rays traded him to the Cincinnati Reds in exchange for Cody Reed, giving him a new path to the majors.
Cincinnati Reds Era (2020–2022)
The Reds added O’Brien to their 40-man roster on November 20, 2020, to protect him from the Rule 5 draft. To open 2021, he was assigned to the Louisville Bats of Triple-A East, where he logged a 7–7 record, a 4.55 ERA, and 121 strikeouts across 112 and two-thirds innings in 23 appearances, including 22 starts.
On September 28, 2021, Cincinnati recalled O’Brien to the active roster to make his MLB debut against the Chicago White Sox. He started the game and threw one and one-third innings, allowing two solo home runs while walking three and striking out two. On April 13, 2022, the Reds designated him for assignment to open a roster spot for Nick Lodolo, ending his time in the Cincinnati organization.
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, with minor league infielder Luis Chevalier later completing the deal. He was designated for assignment on May 27, cleared waivers, and was sent outright to the Triple-A Tacoma Rainiers on June 2, 2022.
O’Brien spent the entire 2023 season in Triple-A with Tacoma. In 51 appearances, he posted a 2.29 ERA with 86 strikeouts and 15 saves across 55 innings, a stretch that rebuilt his stock as a relief pitcher and set the stage for another major league opportunity.
St. Louis Cardinals Era (2023–Present)
On November 5, 2023, O’Brien was traded to the St. Louis Cardinals and added to their 40-man roster. On March 26, 2024, the Cardinals revealed that he had made the Opening Day roster, but a flexor strain landed him on the injured list on March 31, and he was transferred to the 60-day injured list on May 6. He was activated on August 11 and went on to make eight appearances for St. Louis, though he struggled to an 11.25 ERA with 11 strikeouts over eight innings in that initial Cardinals look.
O’Brien was optioned to the Triple-A Memphis Redbirds to begin the 2025 season. On August 4, 2025, he recorded his first career major league win against the Los Angeles Dodgers, and just two days later, on August 6, 2025, he picked up his first career save. He wears uniform number 61 for the Cardinals.
Driving Style and Strengths
O’Brien has reinvented himself as a late-inning relief pitcher, leaning on a strong strikeout rate and the ability to miss bats in tight spots. His 2023 work in Triple-A Tacoma, where he piled up saves while keeping his ERA in the low twos, showcased a swing-and-miss profile that has continued to play in the St. Louis bullpen.
Notable Events and Milestones
His first career MLB win against the Dodgers and his first career save two days later stand as the most memorable early milestones of his Cardinals tenure. Earlier in his career, his Appalachian League Pitcher of the Week honors and a 2018 Midwest League All-Star selection marked him as a prospect on the rise.
Riley O’Brien Career Wins
O’Brien’s win totals reflect a pitcher who has split time between starting and relieving across the minors and majors. His first MLB victory came on August 4, 2025, against the Los Angeles Dodgers, and he added his first MLB save two days later, both in a St. Louis uniform.
MLB Highlights
In his first taste of the majors with Cincinnati in 2021, O’Brien did not record a decision during his September debut. Through the 2025 season’s progress, his breakthrough win and save with the Cardinals have been the defining results of his major league career so far, with the win total continuing to grow as he works out of the St. Louis bullpen.
Other Wins and Performances
Across the minor leagues, O’Brien collected wins at Princeton, Bowling Green, Charlotte, Montgomery, Louisville, and Memphis, and he earned All-Star recognition in the Midwest League in 2018. He also produced a standout 2023 season in Triple-A Tacoma with a 2.29 ERA and 15 saves.
Riley O’Brien Family
Family Background and Racing Lineage
O’Brien comes from a deep baseball family. His grandfather, Johnny O’Brien, played six seasons in the major leagues, and his great uncle Eddie O’Brien also reached the majors, giving Riley a direct connection to long-standing big league tradition.
Personal Life
Riley O’Brien married his wife, Chellyn, on November 18, 2023. He is of Korean descent on his mother’s side, a heritage he has honored by representing the Korean National Team in international competition.
2025 Season Performance
O’Brien began the 2025 season back in the minors with the Triple-A Memphis Redbirds as the Cardinals kept him stretched out and ready. His recall to St. Louis paid off in early August, when he notched his first major league win against the Dodgers on August 4, 2025, and added his first save two days later, signaling a clear step forward in his relief role.
Those milestones arrived at a time when the Cardinals were sorting through late-inning options, giving O’Brien a real opportunity to claim a meaningful place in the bullpen. With each successful appearance, he has built trust in high-leverage spots, and his swing-and-miss stuff has translated into results at the big league level.
Looking ahead within the 2025 campaign, O’Brien is positioned to continue accumulating wins and saves as a multi-inning reliever for St. Louis. His performance in August and beyond has suggested a larger role in the bullpen and a stronger footing in the Cardinals’ plans for the remainder of the year.