Finished No. 4 in the 2025 PGA TOUR University Ranking, earning exempt Korn Ferry Tour membership for the remainder of the 2025 season (top 10 from 2025 PGA TOUR University Eligibility Ranking), as well as an exemption into Final Stage of 2025 PGA TOUR Q-School presented by Korn Ferry (top five from 2025 PGA TOUR University Eligibility Ranking).

Played two seasons at Long Beach State University (2021-23) and transferred to University of Florida for his final two seasons (2023-25). Totaled six collegiate victories, earning four titles at Long Beach State and two at Florida.

Earned All-Southeastern Conference honors both seasons (First Team in 2025, Second Team in 2024), as well as a 2025 All-America Second Team selection in his two seasons at Florida.

Named the 2022-23 Big West Conference Player of the Year and garnered a 2023 All-America Second Team laurel as a sophomore at Long Beach State University.

Won the 2024 Western Amateur. Gilligan’s path to victory included a win over Blades Brown in the Round of 16. In the championship match, Gilligan defeated Florida teammate Jack Turner on the 29th hole (the 11th playoff hole), which made it the longest match in Western Amateur history. Past champions of the Western Amateur include Jack Nicklaus (1961), Andy North (1971), Ben Crenshaw (1973), Phil Mickelson (1991), Justin Leonard (1992, 1993), Tiger Woods (1994), Beau Hossler (2014), Pierceson Coody (2020), and Michael Thorbjornsen (2021).

Won the 2025 Australian Master of the Amateurs. Past champions of the event include PGA TOUR winners Jason Day (2006), Aaron Wise (2016), Kevin Yu (2019), and Sahith Theegala (2020).

Finished T16 at the 2024 Shriners Children's Open on the PGA TOUR, as he became the third amateur to make the cut in the event's history (followed Jack Trent/2019 and Patrick Welch/2022). Earned an exemption for the event via his victory at the 2024 Southern Highlands Collegiate as a junior at Florida.

Made his PGA TOUR debut at the 2024 Barracuda Championship (T40 as a sponsor exemption) between his junior and senior season at Florida.

Represented the United States at the 2024 Arnold Palmer Cup. Teammates included Jackson Koivun and Gordon Sargent, who both earned PGA TOUR membership via PGA TOUR University Accelerated, David Ford, who finished No. 1 in the 2025 PGA TOUR University Ranking, and Michael La Sasso, who earned individual medalist honors at the 2025 NCAA Championship.