O'Brien will start at number eight for her first competitive Ireland appearance since the 2016 Six Nations.

Captain Claire Molloy completes the back-row at openside, with regular skipper Niamh Briggs ruled out of the tournament through injury.

"The squad are very excited to get the tournament under way," said Ireland Women head coach Tom Tierney, ahead of Wednesday's encounter at the UCD Bowl.

"They've had excellent preparation and things have really come together since arriving into UCD on Saturday afternoon, and everyone's been extremely focused on their role and the challenge ahead.

"The Australians are a good team and we'll have to be very good for the opening game. The players are all very clear on the challenges that the Wallaroos pose.

"However, this is a home World Cup and we're confident that the crowd will get behind us tomorrow evening, which will be an added benefit for us, and we're all looking forward to getting the tournament up and running."

Ireland boss Tierney has made four personnel changes and two positional switches from the side that finished the Six Nations earlier this year.

Sophie Spence and Ciara Griffin miss out with Baxter and O'Brien returning, while Paula Fitzpatrick moves from number eight to lock.

Cliodhna Moloney has been preferred to Leah Lyons at hooker for her Women's Rugby World Cup debut.

Ireland Women's team to face Australia Women in Dublin on Wednesday: H Tyrrell (Leinster), E Considine (Munster), J Murphy (Leinster), S Naoupu (Harlequins), A Miller (Connacht), N Stapleton (Leinster), L Muldoon (Ulster), L Peat, C Moloney, A Egan, P Fitzpatrick, M Reilly (all Leinster), A Baxter (Ulster), C Molloy (Bristol, captain), H O'Brien (Munster), Replacements: L Lyons (Munster), R O'Reilly, C O'Connor (both Connacht), S Spencer (Leinster), C Griffin, N Cronin (both Munster), K Fitzhenry (Leinster), M Coyne (Connacht).