As a true freshman at UC Davis in 2017, Whelan played five games, totaling 10 punts for 440 yards.[7] The following year, he appeared in all 13 games while posting 67 punts for 2,756 yards (a 41.1 average), earning honorable mention all-conference honors.[7] Whelan was named third-team all-conference in 2019 while having a 44.1 punting average on 57 kicks.[7][8]
In the 2021 spring season (postponed from 2020 due to COVID-19), Whelan punted 17 times for 815 yards, a Big Sky Conference-leading 47.9 yard average, earning four first-team All-American selections, a first-team all-conference selection, and being named a finalist for the FCS Punter of the Year Award.[8] He handled both punting and kickoff duties in his final year, the fall 2021 season, earning All-Big Sky and second-team All-American honors with a school single-season record 46.25 punting average (his 47.9 average in the prior season did not qualify for the leaderboards due to him having not enough punts).[7][8] He finished his stint at UC Davis with 151 punts for 6,523 yards, having the school all-time record with a 44.01 career punting average.[2][8]
Whelan was selected by the DC Defenders of the XFL with the second pick of the specialists phase in the 2023 XFL Draft.[12] He made the team and served as their punter in all 10 of their games as they went on to be league championship runner-ups, being named All-XFL after having an average of 45.6 yards on 29 attempts.[4][13][14]
Green Bay Packers
On 17 May 2023, Whelan signed with the Green Bay Packers after his time in the XFL,[4] eventually beating out the incumbent Pat O'Donnell for the Packers' punting job.[15][16] He made his NFL debut on 10 September 2023, against the Chicago Bears, recording five punts for 249 yards while becoming the first Irish-born NFL player since the retirement of Neil O'Donoghue in 1985.[16][17][18] After the 2023 season, he was offered a tender.[19]