[5] Sophie is the daughter of Irish World champion and Olympic Silver medallist Sonia O'Sullivan, and Nic Bideau.

[8][9] On 3 February, as part of the University of Washington distance medley relay team, alongside Marlena Preigh, Carley Thomas, and Anna Gibson, she helped the Huskies to victory in the 2023 Bruce Lehane and Scarlet White Women's 4000 m distance medley relay at Boston University Track and Tennis Center, with a 1200 m time of 3.16.24.

[18][19] At the Irish national under 23 Championships in Tullamore, Co. Offaly on 2 July, O'Sullivan scored a double, striking gold at both 800 m (2.10.04)[20] and 1500 m (4.27.02).

[24] In the Women's Senior 1500 m at the Irish National Track and Field Championships on 30 July, she (running in the colours of Ballymore-Cobh) was runner up in a time of 4.12.00, behind Sarah Healy (University College Dublin).

[25] On 4 August, O'Sullivan ran 2.37.08 for the 1000 m, the fastest time in US collegiate history, an Irish under-23 record, and the third fastest time by an Irish woman (behind Sonia O'Sullivan and Ciara Mageen), at the CITIUS Meeting, a World Continental Challenge event, at Stadion Wankdorf in Bern, Switzerland.

[29] O'Sullivan's time was fifth fastest by an Irish woman, with national record holder Ciara Mageen (3.55.87) ranked first.

[30] On 5 September, at the Palio Citta' Della Quercia in Rovereto, Italy, O'Sullivan finished second in the 3000 m in 8.44.72, behind Wubrist Aschal (Ethiopia).

On 18 November, O'Sullivan competed in the NCCA Division 1 Cross Country National championships at Panorama Farms near Charlottesville, Virginia.

[36][37][38] 2024 On 28 January, O'Sullivan opened her indoor season with a third place finish in the mile at the University of Washington/Mile City event at the Dempsey Arena in Seattle.

In the 1500 metres final on 12 May O'Sullivan finished seventh in 4.22.72, behind Washington team mate Chloe Forester, whose winning time was 4.16.33.

[41][42] At the NCCA West Regionals at John McDonnell Field, Fayetteville, Arkansas on 23 May, O'Sullivan placed second in heat 4 in the first round of the 1500 metres in a time of 4.20.35, thereby qualifying for the quarter finals.

[49] On 9 July, at the Cork City Sports at the Munster Technological College in Bishopstown, O'Sullivan ran a time of 9.08.66 to finish 12th in the 3000 metres.

[53] On 6 August O'Sullivan finished 7th in her 1500 m first round heat at the Paris Olympics in a personal best of 4.00.23, behind the winner, Gudaf Tesgaey of Ethiopa (3.58.84).

[58] On 19 October Sophie opened her 2024 cross-country season by finishing 42nd at the Wisconsin pre-nationals, covering the 6K course in 20.10.4, and averaging 5.24.6 per mile.

[59] On 1 November, at the Big Ten Cross-country Championships in Savoy, IL, O'Sullivan was again fifth scorer for the Huskies, as they finished runner up behind Oregon.

[60] At the NCCA West Regional Cross-country at Cofax, Washington on November 15, Sophie finished 33rd position in 20.27 over 6 km and was fifth Huskie over the line, helping the team to take third place behind Oregon and Stanford.