Justice Minister Heiko Maas (Getty)

Justice Minister Heiko Maas has turned his back on Angela Merkel and promised same-sex marriage will be a key issue debated ahead of the 2017 general election.

Maas has expressed his support for marriage equality in an open letter published in honour of the fifth anniversary of the Bundesstiftung Magnus Hirschfeld, a foundation that work towards ending discrimination against the LGBT community.

“We need to defend Magnus Hirschfeld’s legacy with all our might, especially now, as right-wing populists once again wake resentments, make homophobia socially acceptable and want to revive the 1950s’ outdated models of family and society,” he wrote.

“Germany is a strong country, because everyone her can live after their own model of life. To promote this diversity, and to protect it against discrimination, that’s what the Bundesstiftung Magnus Hirschfeld very successfully works for.

“In the future, it can continue to trust in my support, for example when it comes to supporting marriage for everyone,” he added.

Maas was involved in the recent law that would pardon gay men who were prosecuted for homosexuality. However the law has been criticised for not doing enough.

Germany allows same-sex couples to enter into registered life partnerships that provide some of the benefits of marriage – but the Chancellor’s CDU/CSU coalition continues to oppose same-sex marriage.

These partnerships are limited when it comes to adoption.

Maas, who represents the Social Democrats, said they are likely to face opposition from the conservative Christian Democrats, who are part of the coalition government.

Earlier this month research found that Germany has the largest LGBT population in Europe.

The news came from Berlin’s Dalia Research, which published the results of a Europe-wide EuroPulse study, which interviewed 12,000 people across 28 EU countries.

A spokesman for German chancellor Angela Merkel ruled out introducing same-sex marriage last year.