Prime Minister Tony Abbott's sister Christine Forster is determined to marry her fiancee Virginia Edwards in Australia, but concedes she likely faces a ''long engagement''.

Sporting a rainbow tie-dye T-shirt and with her partner by her side, Ms Forster marched with fellow Liberal Party politicians in the Pride March on Sunday.

Christine Forster (right) with her partner Virginia Edwards. Credit:James Boddington

About 30,000 people braved near-40-degree heat to watch the march on Fitzroy Street, St Kilda.

Ms Forster, a Liberal City of Sydney councillor, said the march was a ''wonderful celebration of community, diversity and equality''.