One of Brisbane's leading priests says it's time for Australia's politicians to "step up to the plate" and do their jobs by legislating for marriage equality.

St John's Anglican Cathedral Dean Dr Peter Catt will on Saturday address a marriage equality rally, where he'll be one of several speakers calling for the federal government to hold a free vote for gay marriage.

St John's Anglican Cathedral dean Dr Peter Catt will address a rally on Saturday. Credit:Glenn Hunt

Noting he encounters some opposition from conservatives within his church, but also much more support, Dr Catt said it made no sense to withhold marriage from same-sex couples.

"This is the next evolution," he said. "Marriage has become more and more of a celebration and a commitment of the love between two people."