[7] In December 2020, he scored in his last game at underage level for the club as his side won the League of Ireland U17 Division, beating rivals Shamrock Rovers 2–0 in the final.

[10][11] His competitive debut in senior football came on 20 September 2019, replacing Luke Wade-Slater late on against Derry City at the Ryan McBride Brandywell Stadium.

[15] In January 2021, he signed for the academy of Brighton & Hove Albion,[16][17] who beat fellow Premier League club Liverpool to his signature.

[18] On 24 August 2021, he made his first team debut, replacing Enock Mwepu, in the 81st minute of a 2–0 win away against Championship side Cardiff City in the EFL Cup second round.

[24] Ferguson made a second appearance of the season for the senior side on 8 January 2022, coming on as a 76th-minute substitute where he assisted Jakub Moder's equaliser in the eventual 2–1 – after extra-time — away victory over West Bromwich Albion of the Championship in the FA Cup third round.

[25] Four weeks later, Ferguson made another substitute appearance again coming in the FA Cup, this time away at Tottenham Hotspur on 5 February, in a 3–1 defeat for the Seagulls.

[26] On 19 February 2022, Ferguson made his Premier League debut for Brighton, coming on as a substitute in the 3–0 home loss against bottom side Burnley.

[27] On 24 August 2022, Ferguson scored his first Albion goal himself, set up by fellow academy player Cameron Peupion, in the 90+4th minute of the 3–0 away win over League One side Forest Green Rovers in the EFL Cup second round.

[40] Ferguson brought his season tally to six against Nottingham Forest on 25 November, when he scored in the 26th minute from a Pascal Groß pass to make it 1–1, in a game that Brighton eventually won 3–2.

[44] On 3 February 2025, Ferguson signed for fellow Premier League club West Ham United on loan until the end of the season, rejoining his former coach Graham Potter.

On 27 August 2021, he was called up alongside Brighton teammate Andrew Moran to the Republic of Ireland U21 for the first time, for the 2023 UEFA European Under-21 Championship qualifiers against Bosnia and Herzegovina and Luxembourg.