She seemed an ideal political candidate in a country that likes to call itself the world’s “most successful multicultural nation.”

Tu Le, a young Australian lawyer who is the daughter of Vietnamese refugees, was set to become the opposition Labor Party’s candidate for Parliament in one of Sydney’s most diverse districts. She grew up nearby, works as an advocate for exploited migrant workers and had the backing of the incumbent.

Then Ms. Le was passed over. The leaders of the center-left party, which casts itself as a bastion of diversity, instead chose a white American-born senator, Kristina Keneally, from Sydney’s wealthy northeast to run for the safe Labor seat in the city’s impoverished southwest.

But Ms. Le, unlike many before her, did not go quietly. She and other young members of the political left have pushed into the open a debate over the near absence of cultural diversity in Australia’s halls of power, which has persisted even as the country has been transformed by non-European migration.

While about a quarter of the population is nonwhite, members of minority groups make up only about 6 percent of the federal Parliament, according to a 2018 study. That figure has barely budged since, leaving Australia far behind comparable democracies like Britain, Canada and the United States.

In Australia, migrant communities are often seen but not heard: courted for photo opportunities and as fund-raising bases or voting blocs, but largely shut out of electoral power, elected officials and party members said. Now, more are demanding change after global reckonings on race like the Black Lives Matter movement and a pandemic that has crystallized Australia’s class and racial inequalities.

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The backlash has reached the highest levels of the Labor Party, which is hoping to unseat Prime Minister Scott Morrison in a federal election that must be held by May.

The Labor leader, Anthony Albanese, faced criticism when he held up the white senator, Ms. Keneally, 52, as a migrant “success story” because she had been born in the United States. {snip}

Ms. Keneally, one of the Labor Party’s most senior members, told a radio interviewer that she had “made a deliberate decision” to seek the southwestern Sydney seat. She did so, she said, because it represents an overlooked community that had “never had a local member who sits at the highest level of government, at a senior level at the cabinet table, and I think they deserve that.”

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Ms. Le, 30, said she believed the party leadership sidelined her because it saw her as a “tick-the-box exercise” instead of a viable contender.

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What she finds especially disappointing about Labor’s decision, she said, is the message it sends: that the party takes for granted the working-class and migrant communities it relies on for votes.

Australia has not experienced the same sorts of fights over political representation that have resulted in growing electoral clout for minority groups in other countries, said Tim Soutphommasane, a former national racial discrimination commissioner, in part because it introduced a “top down” policy of multiculturalism in the 1970s.

That has generated recognition of minority groups, though often in the form of “celebratory” multiculturalism, he said, that uses food and cultural festivals as stand-ins for genuine engagement.

When ethnic minorities get involved in Australian politics, they are often pushed to become their communities’ de facto representatives — expected to speak on multiculturalism issues, or relegated to recruiting party members from the same cultural background — and then are punished for supposedly not having broader appeal.

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