He will sing his club anthem Dizzy at this year’s Eurovision Song Contest in Malmö, Sweden, on May 11.
Alexander is hoping to improve on Britain’s disappointing performance last year, when Mae Muller came second last.
Dizzy was co-written by Alexander and Danny L Harle, who has produced hits for Dua Lipa, Chic and Charli XCX.
Alexander, who now releases music under his own name, is already known across Europe as the former frontman of the band Years and Years who had hits such as Desire, King and If You’re Over Me.
The singer is a seasoned artist with a large fan base, having scored five UK top 10 singles and two number one albums over the past decade with the band.
He is also a Bafta nominated actor, having played the lead role in Channel 4’s hard-hitting AIDS drama It’s A Sin.