Growing up, practiced at the nine-hole Chevy Chase Country Club in Glendale, California. Never let himself hit off mats to avoid giving himself a flat lie.

Graduated from University of California-Berkeley in May of 2019 with a bachelor's degree in business administration from the Haas School of Business, which ranked third on the 2020 U.S. News and World Report for Best Undergraduate Business Programs. On September 27, 2021, Cal announced the creation of two endowed scholarships to honor the legacies of Morikawa and Max Homa and their contributions to the Cal men's golf program. "I owe a lot to Cal golf. It was a huge four years of my life that I would never trade in for anything."

As a little kid, his dream was to throw out the first pitch at a Los Angeles Dodgers game. On September 3, 2019, his wish came true, as he threw out the first pitch and called it one of the “most memorable moments in my life.”

Parents are Blaine and Debbie. Blaine is Japanese-American from Hawaii and Debbie is Chinese-American from California.

Played four seasons at Cal (2015-19), where he was a four-time All-American with first-team honors each of his final three seasons (2017, 2018, 2019). Named the 2018-19 Pac-12 Conference Player of the Year, following Michael Kim (2013) as the second player in program history to earn the award. Also named the 2015-16 Pac-12 Conference Freshman of the Year. Earned five individual victories (and lost playoffs on two other occasions) at Cal, with the crown jewel being medalist honors at the 2019 Pac-12 Championship, where he became the fourth Cal player to win the individual conference title (Max Homa/2013, Eric Mina/2010, Charlie Wi/1995).

Between his freshman and sophomore seasons at Cal, nearly won his first start in a professional tournament -- the 2016 Wichita Open on the Korn Ferry Tour -- but fell to J.J. Spaun and eventual champion Ollie Schniederjans in a playoff. Morikawa earned a sponsor exemption for the Korn Ferry Tour event by virtue of his victory at the 2015 Trans-Mississippi Amateur Championship, which was contested in nearby Andover, Kansas. At the 2016 Wichita Open, Morikawa made the cut on the number, carded back-to-back 63s on the weekend, and forced a playoff as he played the final five holes of regulation in 5-under par (eagle-birdie-birdie-par-birdie).

Rose to No. 1 and spent three weeks atop the World Amateur Golf Ranking in May 2018.

As a junior at Cal, posted a 68.68 scoring average for the 2017-18 season, which broke the NCAA all-time record for single-season scoring average.

Notable amateur victories included the 2015 Trans-Mississippi Amateur Championship, 2016 Sunnehanna Amateur, 2017 Northeast Amateur Invitational. Past champions of the Trans-Mississippi Amateur Championship include Jack Nicklaus (1958, 1959), former PGA TOUR commissioner Deane Beaman (1960), Ben Crenshaw (1972), Gary Koch (1973), Bryson DeChambeau (2013), Will Zalatoris (2014, 2016), and Cameron Champ (2017).

Qualified for match play at three consecutive U.S. Amateur Championships in 2016 (Oakland Hills Country Club in Bloomfield Hills, Michigan), 2017 (The Riviera Country Club in Pacific Palisades, California), and 2018 (Pebble Beach Golf Links). Reached the Round of 16 in both 2016 and 2017. Fell to future PGA TOUR winner Kevin Yu in the Round of 16 at the 2017 U.S. Amateur at The Riviera Country Club.

Won the 2013 Western Junior Championship -- the oldest national junior tournament in the United States. Past champions of the event include Jim Furyk (1987) and Rickie Fowler (2005).