Grew up playing golf at River Creek Club in his longtime hometown of Leesburg, Virginia.

Attended The Academies of Loudoun, a STEM-focused high school which he had to test into during middle school. Michael loved math and science, so he studied engineering at the school's Academy of Engineering and Technology. Played his high school golf at nearby Tuscarora High School.

Hoped to continue studying engineering in college, but realized throughout the recruiting process the demands of college golf would conflict with such a rigorous major, so he shifted his focus to economics upon enrolling at Wake Forest University.

Roughly 12 years after retiring and leaving the real estate industry, Michael's mother, Shannon, earned an expert rules certification from the USGA and became a volunteer on the Middle Atlantic Golf Association Rules Committee. Shannon, who scored over a 90 on her rules exam, has served as a rules official for collegiate and amateur tournaments in the region. Michael remembers Shannon studying for her exams by constantly quizzing the family with different rules scenarios.

Hardly ever read for leisure in high school or college, but one of his professors and close friends, Michael Sloan, encouraged Brennan to pick up books for many years. Brennan and Sloan grew close through their shared love of golf and Sloan’s Greek mythology course. In 2025, Brennan created a Goodreads account to track his reading history and identify what he wants to read next. Two of Brennan’s favorite books – “Island of the World” and “The Lighthouse” – were written by Michael O’Brien, and he hopes to read all of O’Brien’s books.

Had an NIL partnership with Tom Brady's clothing brand (BRADY) -- which later became part of NOBULL -- during his college career at Wake Forest. Brennan and University of Texas golf star Cole Hammer were both featured in a 2022 video with Brady announcing the brand's launch of its golf-specific apparel. Brennan got to do the shoot with Brady and meet the seven-time Super Bowl champion.

Active on Letterboxd, a social media platform used by movie fans to rate movies, share reviews, and create both rankings and watchlists. In college, Brennan and his friends and teammates got together weekly to watch movies, and they managed an Excel spreadsheet to select movies for the group to watch.

Fan of the Washington, D.C. sports teams, with his favorites being the Commanders (NFL football) and Nationals (MLB baseball).

Finished No. 12 in the 2024 PGA TOUR University Ranking after four seasons at Wake Forest University. Performance benefits included exempt membership for the remainder of the 2024 PGA TOUR Americas season, as well as an exemption to Second Stage of 2024 PGA TOUR Q-School presented by Korn Ferry.

Played four seasons at Wake Forest University (2020-24), where he earned eight individual victories, highlighted by back-to-back wins at the 2023 and 2024 Atlantic Coast Conference Championships. Brennan’s collegiate victories also included the 2021 Wake Forest Invitational contested at Pinehurst No. 2. Brennan’s eight wins were tied with 17-time PGA TOUR winner Curtis Strange for third in program history, only behind three-time PGA TOUR winner Gary Hallberg (nine) and 2011 FedExCup champion Bill Haas (10).

With Wake Forest men’s golf head coach Jerry Haas as his caddie, Brennan played alongside PGA TOUR winner and fellow Wake Forest alum Will Zalatoris as he won the 2022 Genesis Invitational Collegiate Showcase at The Riviera Country Club, which earned him an exemption for the PGA TOUR’s 2022 Genesis Invitational.

Totaled a 71.46 career scoring average across his four seasons at Wake Forest, which, upon exhaustion of his eligibility, ranked fourth in program history in records dating back to 1981. Brennan’s average only trailed Alex Fitzpatrick (70.94 from 2018-22), 2011 FedExCup champion Bill Haas (70.87 from 2000-04), and PGA TOUR winner Will Zalatoris (70.44 from 2015-18).

Represented the United States at the 2022 Arnold Palmer Cup.

Won three consecutive Middle Atlantic Amateur Championships (2017, 2018, 2019). Past champions of the event include PGA TOUR winner Billy Hurley III (2004), 21-time TOUR winner Davis Love III (1984), eight-time TOUR winner Fred Funk (1979), and former PGA TOUR commissioner Deane Beman (1962, 1963).

Won the 2019 Virginia State Golf Association Amateur Championship. Past champions of the event include 21-time PGA TOUR winner Lanny Wadkins (1970), 17-time TOUR winner Curtis Strange (1974, 1975), three-time TOUR winner John Rollins (1997), and TOUR winner Billy Hurley III (2004, 2005).

Qualified for match play at the 2019 U.S. Junior Amateur Championship contested at Inverness Club in Toledo, Ohio, where he lost to eventual champion Preston Summerhays in the Round of 32.