Moved from Australia to the United States at age 11; he attended a golf academy in Hilton Head Island, South Carolina for the first three years, then spent the next four years at Saddlebrook Preparatory Academy in Wesley Chapel, Florida.

Shortly after his seventh birthday in August 2008, with the help of his dad, Paul, started a YouTube channel (@KarlGolf) dedicated to his golf journey. In his childhood, the channel helped Karl gain more exposure internationally, and even helped he and his father raise money to travel to the United States for the U.S. Kids Golf World Championship and Junior World Championships.

Devoted fantasy football manager.

Finished No. 10 in the 2024 PGA TOUR University Ranking after four seasons at Stanford University, earning conditional membership for the remainder of the 2024 Korn Ferry Tour season, fully exempt membership for the remainder of the 2024 PGA TOUR Americas season, and an exemption to Second Stage of 2024 PGA TOUR Q-School presented by Korn Ferry.

Played four seasons at Stanford University (2021-24), where he earned a 2024 All-America Second Team honor, three All-Pac-12 Conference laurels (First Team in 2023 and 2024, Second Team in 2022), and earned his lone collegiate victory at the 2024 Pac-12 Championship.

Concluded his collegiate career ranked No. 5 in Stanford history in career scoring average (71.04), trailing Tiger Woods (70.96), Michael Thorbjornsen (70.40), Patrick Rodgers (70.31) and school record holder Maverick McNealy (70.12).

Qualified for the 2023 U.S. Open between his junior and senior seasons at Stanford.

Just under a month before his 16th birthday, won the 2017 Southern Amateur Championship at The Country Club of North Carolina in Pinehurst. Notable past winners of the Southern Amateur include Bobby Jones (1917, 1920, 1922), Ben Crenshaw (1971, 1973), Justin Leonard (1992, 1993), Webb Simpson (2005, 2007), and Harris English (2011).

Notably recorded runner-up finishes at the 2017 and 2018 Western Junior Championships, the 2022 Northeast Amateur Invitational, and the 2023 North and South Amateur Championship at Pinehurst Resort & Country Club (fell to future PGA TOUR winner Nick Dunlap in the championship match of the North and South).

In summer 2019, qualified for match play at the Western Amateur Championship, and reached the quarterfinals of the 2019 U.S. Amateur Championship at Pinehurst Resort & Country Club; he was eliminated from the U.S. Amateur on his 18th birthday.

Also qualified for match play at the 2021 Western Amateur and 2023 U.S. Amateur.

Represented Australia at the 2023 World Amateur Team Championship, helping his country to a co-runner-up finish.

Played for the International Team, captained by fellow Australian Stuart Appleby, at the 2019 Junior Presidents Cup at Royal Melbourne Golf Club. South Africa's Christo Lamprecht was also a member of the 2019 International Team.

Gold medalist at the 2018 Summer Youth Olympics, finishing two strokes ahead of silver medalist Akshay Bhatia at Hurlingham Club in Argentina.

Enjoyed a strong record at the Junior PLAYERS Championship, recording five consecutive top-10s and improving his finish every year: T9/2016, T8/2017, 6th/2018, 3rd/2019, T2/2020.

Also had an impressive record at the AJGA's Rolex Tournament of Champions, finishing third in 2018 and second in 2019.