Has used a 10-finger grip nearly his entire career; he tried overlap, but it made him feel like he had "no control over the club," and when he tried interlock it hurt his knuckles.

Hit the first tee shot at the 2022 U.S. Open at The Country Club in Brookline, Massachusetts; his hometown of Wellesley, Massachusetts is less than 10 miles from The Country Club.

Born in Cleveland, Ohio and spent a little over four years there before the family moved to Massachusetts in 2006.

After three years at IMG Academy, returned to his hometown of Wellesley, Massachusetts and graduated from Wellesley High School in 2020; he played the fall 2019 season on the golf team and finished as the individual runner-up at the Division 1 State Championship (18-hole event), one stroke behind medalist Weston Jones.

Earned the nickname of "Thunder Cub" while at IMG Academy; the coach there told Michael his last name translated to "Son of a Thunder Bear" and the nickname stuck.

Mother, Sandra, played golf at Ursuline College, which was an NAIA program (now NCAA Division II) in Pepper Pike, Ohio, less than 15 miles east of Cleveland.

Finished No. 1 in the 2024 PGA TOUR University Ranking after four seasons at Stanford University, following Texas Tech University's Ludvig Åberg (2023) as the second player in history to earn PGA TOUR membership via a No. 1 finish in their respective PGA TOUR University classes. Thorbjornsen earned TOUR membership for the remainder of the 2024 season, as well as the 2025 season by virtue of his No. 1 finish.

Reached as high as No. 2 in the World Amateur Golf Raking.

Played four seasons at Stanford University (2021-24), where he was named the 2023 Pac-12 Conference Golfer of the Year and earned three collegiate victories, including individual medalist honors at the 2023 Pac-12 Championship -- which helped the Cardinal win their first team conference title since 2019.

Finished third in program history with a 70.40 career scoring average in his four seasons at Stanford, only trailing record holder Maverick McNealy (70.12) and Patrick Rodgers (70.31). Notably posted a 69.26 scoring average for the 2022-23 season as a junior, which, at the time, was the second-lowest single-season scoring average in program history, only trailing McNealy's school record of 69.05 from the 2014-15 season.

In addition to being named 2023 Pac-12 Conference Golfer of the Year, honors at Stanford included three All-America laurels (First Team in 2023 and 2024, Second Team in 2022) and three All-Pac-12 First Team selections (2022, 2023, 2024).

Made the cut at the 2019 U.S. Open at Pebble Beach Golf Links at 17 years, 8 months, 29 days of age, becoming the second-youngest player to make the cut at a U.S. Open since World War II. The only other player under the age of 18 to make the cut at a U.S. Open at the time was Beau Hossler (17 years, 3 months) in 2012.

Finished solo-fourth at the 2022 Travelers Championship as an amateur, marking the first top-five by an amateur on the PGA TOUR since Braden Thornberry at the 2017 FedEx St. Jude Classic (T4). Also recorded a top-25 at the 2023 John Deere Classic (T17) as an amateur.

Won the 2021 Western Amateur at Glen View Club in Golf, Illinois with a 4-and-3 victory over Gordon Sargent in the championship match. Also earned medalist honors in stroke play and defeated Austin Greaser (semifinals), Ricky Castillo (quarterfinals), and Maxwell Moldovan (Round of 16) en route to the title. Later qualified for match play at the 2022 and 2023 Western Amateur, but lost in the Round of 16 both times.

Two weeks prior to his victory at the 2021 Western Amateur, won the 113th Massachusetts Amateur Championship. Defeated Matt Parziale, the 2017 U.S. Mid-Amateur champion, in the 36-hole final, making 18 birdies across 30 holes en route to an 8-and-6 victory.

Won the 2018 U.S. Junior Amateur Championship at Baltusrol Golf Club, defeating Akshay Bhatia (1 up) in the championship match. Notably defeated Joe Highsmith in the quarterfinals. Became the first Massachusetts resident to win the event since Brett Quigley in 1987.

Qualified for the 2022 and 2023 U.S. Opens while still an amateur (missed cut at both).

Recorded top-25s at the Hero Dubai Desert Classic on the DP World Tour in 2023 (T20) and 2024 (T11).

Qualified for match play at three consecutive U.S. Amateur Championships from 2020 through 2022. Advanced to the quarterfinals in 2020 at Bandon Dunes Golf Resort with wins over Trent Phillips (Round of 64), Hugo Townsend (Round of 32), and Mateo Fernandez de Oliveira (Round of 16). Fell to Nick Gabrelcik in the Round of 32 in 2021 at Oakmont Country Club. Lost in the Round of 64 in 2022 at The Ridgewood Country Club in Paramus, New Jersey.

Represented the United States in international competition at the 2022 World Amateur Team Championship (Eisenhower Trophy), 2022 Arnold Palmer Cup, 2019 Junior Presidents Cup, and 2018 Junior Ryder Cup.

Along with teammates Austin Greaser and Gordon Sargent, helped the United States to a third-place finish at the 2022 World Amateur Team Championship (Eisenhower Trophy), contested at Le Golf National in France.

Partnered with Rose Zhang for two matches (1-1 record) at the 2022 Arnold Palmer Cup, and won his singles match over Frederik Kjettrup for a 2-2 overall record for the event.

Named a 2018 AJGA All-America First Team selection; the other first-team honorees included PGA TOUR winner Akshay Bhatia and Korn Ferry Tour winner Ricky Castillo.