A gay politician who is running for the Labour leadership in New Zealand has selected a former Mormon to be his deputy.

Out politician Grant Robertson is running to become leader of the Labour party, after current leader David Cunliffe agreed to trigger a leadership challenge and seek a new mandate.

Mr Robertson last week announced Jacinda Ardern – a former member of The Church of Jesus Christ of Latter-day Saints – as his running mate.

Ms Ardern revealed during a debate on the country’s equal marriage bill last year that she had previously been a Mormon, recounting: “[I was] a staunch member of the Labour Party, but I was also at that time a member of the Mormon Church. It is fair to say that I know what cognitive dissonance feels like.

“When I started campaigning for civil unions some time later, I decided that I could not sustain such competing value sets any longer, and I left the Church.

“My battle was never over choosing equality or not, but rather how to deal with the fact that the values of equality and fairness were in fact the only things I never ever doubted.”

Selecting her at his campaign launch, Mr Robertson told TVNZ: “This is about a new generation to win. The person I will be recommending to the Labour caucus to be deputy leader is Jacinda Ardern.”