In 2013, Martin was invited to be part of the metal opera project Avantasia, by Tobias Sammet. Martin played the role of a beggar on the album "The Mystery of Time", performing "What's Left of Me," with Sammet. Martin was also part of their 2013 world tour in support of the album as one of the guest vocalists. He is also part of their 2016 world tour in support of the album "Ghostlights", notably performing the guest vocal role in the songs "Dying for an Angel", "The Wicked Symphony" and "Twisted Mind".