 On 14 February 2013, McCallister announced that he had resigned from the UUP due to its decision to engage in an electoral pact with the Democratic Unionist Party.He was a co-founder of the NI21 party with fellow ex-UUP member Basil McCrea but resigned the following year following disputes with McCrea.He re-contested his seat as an Independent at the 2016 election but lost his seat, receiving just 2.8% of the vote.