Sean Guenther Bio
Sean McManus Guenther (born December 29, 1995) is an American professional baseball pitcher who is currently in the Detroit Tigers organization. A left-handed relief pitcher, Guenther has competed in Major League Baseball (MLB) for both the Miami Marlins and the Detroit Tigers. Originally from Atlanta, Georgia, he developed into a draft prospect at the University of Notre Dame and was selected in the seventh round of the 2017 MLB Draft by the Marlins. After working his way through the minors, he made his MLB debut in 2021 and has since navigated promotions, injuries, and roster moves while continuing his professional career.
Early Life and Background
Sean McManus Guenther was born on December 29, 1995, in Atlanta, Georgia, and grew up in the metropolitan area. He attended Marist School in Brookhaven, Georgia, graduating in 2014. At Marist, he played baseball and developed into a college-ready pitching prospect.
During the summer of 2014, Guenther played collegiate-style amateur baseball for the Brookhaven Bucks in the Sunbelt Baseball League. The experience helped him refine his craft before he enrolled at the University of Notre Dame, where he joined the Fighting Irish baseball team.
Path to Baseball
At Notre Dame, Guenther made an immediate impact as a freshman in 2015, posting a 1–3 record with a 2.72 ERA and a 1.295 WHIP while leading the Irish with five saves. His performance earned him Louisville Slugger Freshman All-American honors and a place on the ACC All-Freshman Team. As a sophomore in 2016, he appeared in 15 games with 11 starts, recording a 3–5 record and a 4.62 ERA.
Following the 2016 season, Guenther played collegiate summer baseball for the Orleans Firebirds of the Cape Cod Baseball League. In his junior year at Notre Dame, he went 2–6 with a 2.64 ERA, a 1.328 WHIP, and seven saves. After that junior season, the Miami Marlins selected him in the seventh round, 209th overall, of the 2017 MLB Draft.
Sean Guenther Career
Early Career (2017–2019)
Guenther began his professional career in 2017 with the Gulf Coast League Marlins of the Gulf Coast League, where he allowed only one run with eleven strikeouts in 11 innings across four games. He was quickly promoted to the Batavia Muckdogs of the New York-Penn League, posting a 1–4 record with a 3.83 ERA and 33 strikeouts in 40 innings.
In 2018, Guenther was assigned to the Jupiter Hammerheads of the Florida State League. After early struggles he was demoted to the Greensboro Grasshoppers of the Single-A South Atlantic League, and he also appeared in a rehab game with the GCL Marlins. In 2019, he pitched for both the Clinton LumberKings of the Midwest League and the Jupiter Hammerheads. He did not appear in any games in 2020 because the minor league season was canceled due to the COVID-19 pandemic.
Miami Marlins Era (2021)
Guenther opened the 2021 season with the Pensacola Blue Wahoos of Double-A South, going 1–0 with a 1.02 ERA and 28 strikeouts in 17 2/3 innings. On June 8, he was promoted to the Jacksonville Jumbo Shrimp of Triple-A East, and on August 4, the Marlins called him up to the major leagues. He made his MLB debut two days later.
On April 7, 2022, Guenther underwent Tommy John surgery, which ended his season before it began and kept him out of action for an extended period.
Detroit Tigers Era (2022–Present)
On November 2, 2022, Guenther was claimed off waivers by the Detroit Tigers. He was removed from the 40-man roster on November 15 and sent outright to the Triple-A Toledo Mud Hens. He spent time in Toledo working back from injury before rejoining the major league club.
Guenther began the 2024 campaign with Toledo, recording a 3.86 ERA with 46 strikeouts and three saves across 44 1/3 innings. On August 1, 2024, the Tigers selected his contract and added him to the active roster. He made his season debut that day against the Kansas City Royals, relieving Brenan Hanifee with two outs in the eighth inning. Over 17 appearances with Detroit in 2024, he went 3–0 with a 0.86 ERA and 12 strikeouts in 21 innings.
To begin the 2025 season, Guenther was optioned to Triple-A Toledo. On July 6, 2025, he was placed on the 60-day injured list after undergoing left hip arthroscopy. In nine appearances for Detroit in 2025, he went 0–1 with a 5.23 ERA and eight strikeouts across 10 1/3 innings. He was designated for assignment by the Tigers on November 18 and was non-tendered on November 21, becoming a free agent. On December 16, 2025, Guenther re-signed with the Tigers on a minor league contract.
Driving Style and Strengths
Guenther works as a left-handed relief pitcher, and his strengths show up most against same-handed hitters. His 0.86 ERA across 21 innings for Detroit in 2024 highlighted the value he brings in short stints when he is healthy. He has handled a variety of roles in the minors, including starting and closing, giving managers flexibility in how they deploy him.
Notable Events and Milestones
Guenther’s MLB debut came with the Miami Marlins in August 2021 after a strong start at Double-A and Triple-A. He later underwent Tommy John surgery in April 2022, a major setback that he worked through before returning to the majors with the Tigers in 2024. His 2024 stretch run with Detroit, marked by 17 scoreless-leaning appearances, stands as the most consistent run of his MLB career.
Sean Guenther Career Wins
Sean McManus Guenther’s MLB career includes three wins through the 2025 season. His first MLB action came with the Miami Marlins in 2021, and his most productive major league stretch has come with the Detroit Tigers beginning in 2024.
MLB Highlights
Through the 2025 season, Guenther has posted a 3–2 record with a 5.05 ERA and 35 strikeouts in his MLB career. His first full MLB opportunity came in 2024 with Detroit, when he went 3–0 with a 0.86 ERA in 17 appearances. His 2025 season was limited by a left hip injury, and he finished with an 0–1 record and a 5.23 ERA in nine appearances for the Tigers.
Other Wins & Performances
At Notre Dame, Guenther earned Louisville Slugger Freshman All-American honors and was selected to the ACC All-Freshman Team in 2015. In the minor leagues, he reached Triple-A with Jacksonville in 2021 and Toledo in 2024 and 2025, and he recorded saves at multiple minor league stops during his development.
Sean Guenther Family
Family Background and Racing Lineage
Public information about Sean McManus Guenther’s immediate family, parents, and siblings is limited and not detailed in available sources.
Personal Life
Guenther is an American baseball pitcher originally from Atlanta, Georgia, who attended Marist School and the University of Notre Dame. Verified public details about a spouse, partner, or children are not currently available.
2025 Season Performance
Sean McManus Guenther began the 2025 season at Triple-A Toledo after a strong finish with Detroit in 2024. He was called up by the Tigers and appeared in nine games at the major league level, logging a 0–1 record with a 5.23 ERA and eight strikeouts over 10 1/3 innings.
On July 6, 2025, Guenther was placed on the 60-day injured list after undergoing left hip arthroscopy, ending most of his 2025 campaign. The Tigers designated him for assignment on November 18 and non-tendered him on November 21, making him a free agent.
On December 16, 2025, Guenther re-signed with the Tigers on a minor league contract, keeping him in the Detroit organization as he works back from injury. His next steps will likely focus on returning to health and earning another opportunity in the Tigers’ bullpen.