He played junior rugby league for the Leeton Greenies and Gungahlin Bulls, before being signed by the Canberra Raiders.

When the NRL announced its annual Academic Team of the Year for 2023 in recognition of the educational achievements of current players off-field, Nicholls' academic record included a Graduate Certificate of Program Management from Queensland University of Technology (2021), a Diploma of Business from Australian Vocational Training Company (2013) and a Bachelor of Sport Management & Coaching Science from the University of Canberra (2012).

[19][20][21][22] In round 10 of the 2020 NRL season, Nicholls scored his first try for South Sydney in their 18–20 loss to the Newcastle Knights at Bankwest Stadium.

[25] In round 25, he was named captain for the match against St. George Illawarra, after South Sydney chose to rest Adam Reynolds in the lead-up to the finals.

[31] During that match, he broke a thumb and subsequently underwent surgery to stabilise the joint, rendering him unfit to play for the next few weeks.

[32] Nicholls next played in round 13 and scored a try for the Dolphins in their 26–12 victory over the St. George Illawarra Dragons at Kayo Stadium.

[34] In September, the Dolphins' Inaugural Presentation Ball was held at Brisbane Convention and Exhibition Centre, and Nicholls received the club's annual Best Forward award.

[37] On 2 November 2019, Nicholls married professional model and executive assistant Perrie Davis in the Great Hall at the University of Sydney.