Diagnosed with breast cancer at age 25, Mary Doyle thought her future had come to a halt.

“I felt like someone had punched me,” she recounted in her first speech to the House of Representatives on Thursday.

“How can I have cancer? I’m too young – this can’t be real.”

Almost 30 years later, the new Labor MP for the seat of Aston has become the first woman to represent the outer-Melbourne electorate in its history.

As Ms Doyle described her medical battles and modest upbringing, she paid tribute to Australia’s public healthcare system and social security net for helping her overcome cancer and afford her opportunities to succeed.

The former union official held back tears as she pledged to keep Medicare strong for Australians who come after her.

“My backstory is one riddled with challenges,” she said.

“Those on the other side talk about opportunity while denying families like mine any assistance to grasp those opportunities.

“Labor governments understand this … and the one I’m now a part of is no different.

“No one held back. No one left behind.”

The youngest of nine children born to Catholic parents, Ms Doyle recalled a childhood of deprivation.

After her father lost his job to alcoholism, the family relied on the invalid pension and public housing, sparking a passion for social justice.

Ms Doyle’s election to Aston in April was the first time a government has won a seat off the opposition at a by-election in over 100 years.

Her accession to parliament, following the resignation of former Liberal minister Alan Tudge, extended the government’s majority in the lower house to a more comfortable 78 out of 151 seats.

Ms Doyle, a republican, has another distinction to her name – last month she became the first parliamentarian to swear allegiance to King Charles.

– AAP