He said an opinion poll showed 58 per cent of Scots favoured the move, with 19 per cent opposed.
He claimed support was widespread among political parties: "Civil partnership was an important step, giving same-sex couples much the same legal rights and responsibilities as everyone else. But there have always been some people who want to portray those couples as second-class citizens.
"Full legal equality for same-sex couples who want to marry and for mixed-sex couples who want civil partnership instead would be much more in keeping with this increasingly inclusive Scottish public opinion.
"I believe there are enough supporters in all political parties for it to be changed during the next Parliament."