In 2014, O'Neill and his father Peter O'Neill both scored centuries in the same North West Metro Cricket Association match for the Flemington Colts. Peter retired not out on 106, while Fergus was eventually caught for 104.[4] Fergus attended Maribyrnong College, a sports secondary school in Melbourne.[4]
A bowling all-rounder, O'Neill plays for Melbourne in Victorian Premier Cricket. In 2019 he took a hat-trick against Monash, finishing with career-best figures of 6/25.[5] In the 2021–22 season he received the Paul Sheahan Club Champion Award for his all-round performance, averaging 19.31 with the ball and 42.33 with the bat that year.[6]
O'Neill's performances in Premier cricket earned him a List A debut for Victoria later that season, as well as a first-class appearance for Victoria the following season in which he took four wickets on debut, including the wickets of Australian Test players Alex Carey, and Travis Head (twice).[7] In Victoria's victory over South Australia in the 2023–24 Sheffield Shield, he took five wickets in each innings.[8]
O'Neill was named 2024–25 Sheffield Shield player of the season after taking 38 wickets at an average of 21.07.[9]
He signed for Nottinghamshire County Cricket Club to play in the opening four rounds of the 2025 County Championship.[10][11] O'Neill took 5/81 in the first innings of his debut match against Durham.[12] In his third outing for Nottinghamshire, he claimed new First Class career-best figures of 5/19 in the first innings against Warwickshire.[13] At the end of his stint, he was the leading wicket taker in the Championship with 21 wickets at an average of 17.9.[14]
In November 2025, O'Neill agreed a contract with Nottinghamshire which will see him play County Championship matches for the club from April to June in both 2026 and 2027.[15][16]
With O'Neill's contracts with Victoria and the Melbourne Renegades expiring at the end of the 2025-26 season, it was widely reported that he had received and was considering offers from New South Wales and the Sydney Sixers.[17] O'Neill accepted the move to the Sixers for the Big Bash, signing a two year deal,[18] however chose to remain with Victoria on a three-year contract.[19]
