Former ACTU president Ged Kearney unexpectedly fought off the Greens in Saturday's by-election with a swing towards Labor, a poll which was brought on by former Labor MP David Feeney having to step-down over his citizenship status.

Treasurer Scott Morrison said the Batman election was about a race to the left and the Labor party won.

"They are the most left political party in the country," Mr Morrison told Sky News on Sunday.

"I wouldn't describe Batman as a mainstream electorate and if Bill Shorten wants to run the campaigning he ran in Batman around the rest of the country, I'd say 'bring it on Bill'."

But Labor frontbencher Mark Butler thought the prime minister took a cynical approach to the seat by sitting out the contest and hoping it would see a Greens MP elected into parliament.

"That didn't come off," Mr Butler told ABC radio.

"This is a great victory for Bill Shorten and Labor, a real credit to Ged Kearney and I can't imagine a better candidate that we could have run in that seat."

Mr Shorten on Saturday night said the win meant Labor was "back", having proved bookmakers and commentators wrong for writing them off in Batman.

With the Liberals not fielding a candidate in Batman, the by-election was a test of whether the Greens' march into inner-metropolitan seats would continue, or if Labor could successfully appeal to a younger demographic.

"Labor hears the lesson and message of Batman," Mr Shorten said.

"More than ever before Labor has to battle the perception that the major parties and political insiders are only in this for themselves."

The minor party blamed their loss on preferences to "hard-right" parties such as the Australian Conservatives.

Ten candidates contested the by-election.

Six-time Greens candidate Alex Bhathal did not say if she'd run again for the seat after conceding defeat.

Australian Associated Press