[2] Ainslie was the Green candidate for the new constituency of Streatham and Croydon North in the 2024 United Kingdom general election,[3] coming in second place with 17.1% of the vote.

After graduating he studied at the drama school Mountview Academy of Theatre Arts on a scholarship.

[8][9] Ainslie has been a Green Party Councillor in the London Borough of Lambeth since 2014, representing the St Leonard's Ward.

[11][12] In the European Parliament, Ainslie was a member of the Committee on Transport and Tourism, and was part of the delegation to the ACP–EU Joint Parliamentary Assembly.

[5] In the 2019 general election, Ainslie was the Green Party candidate for the South London-based seat of Streatham, where he finished in fourth with 4.5% of the vote.