[4] He joined Hearts aged 12, progressing through their youth teams until on 31 August 2013, he made his senior debut for the club, coming on as a 74th-minute substitute in a Scottish Premiership match against Inverness Caledonian Thistle, replacing Jamie Walker in a 2–0 defeat.

[6] On 16 June 2014, Nicholson signed a new three-year contract extending his stay until the summer of 2017, following the club's relegation to the Scottish Championship.

He scored his first goal of the season against Hibs in the Edinburgh Derby; a solo effort after he nutmegged Scott Robertson and hit a left-footed drive beyond the keeper.

On 28 June 2017, it was confirmed that Nicholson agreed to a contract with MLS side Minnesota United FC, and would be eligible to join the team on 10 July 2017.

[21] On 31 May 2024, Motherwell announced that they had signed Nicholson to a permanent two-year contract, after he'd initially joined the club on loan from Colorado Rapids.