Simon Kennedy, who replaced former Liberal prime minister Scott Morrison after his retirement from politics, has been officially sworn in on Tuesday.
Mr Kennedy was elected to Mr Morrison's old seat of Cook in Sydney's south in April with a first preference vote of more than 60 per cent.
Opposition Leader Peter Dutton welcomed Mr Kennedy to the parliamentary team.
"Simon has done an exceptional job in bringing together the local community and I congratulate him on his success," he said.
Greens senator Steph Hodgins-May was also sworn into parliament on Tuesday against the backdrop of the federal budget.
The Victorian senator has taken on the role of Greens spokeswoman for science and early childhood education.
She pledged to fight for free early childhood education and care.
"In this cost of living crisis, early childhood education and care is too expensive and too hard to access," she said.
"As a result, women are missing out on paid work and they're being left behind because they can't afford care for their children."
Her predecessor Janet Rice marked the handover on the lawns of Parliament House with a baton before setting off on an 850km bike ride back to Melbourne across 17 days.
