Incumbent US Senator Edward Markey speaks in Malden, Massachusetts, on Sept 1, 2020 after defeating US Representative Joe Kennedy III in the Massachusetts Democratic Senate primary. (MICHAEL DWYER / AP)

WASHINGTON - US Progressive Democratic Senator Ed Markey, who advocates combating climate change and the passage of the Green New Deal, defeated House Representative Joe Kennedy III in the Massachusetts Senate primary on Tuesday, showing the progressive strength that is reshaping the Democratic Party.

"Tonight is more than just a celebration of a movement. It is a real reaffirmation of the need to have a movement, a progressive movement of young people demanding radical change, demanding justice," Markey, 74, told supporters in his hometown of Malden.

Tonight is more than just a celebration of a movement. It is a real reaffirmation of the need to have a movement, a progressive movement of young people demanding radical change, demanding justice.

Ed Markey, US progressive senator

The senator's campaign slogan reads, "It's not your age -- it's the age of your ideas that's important." His rival Kennedy III is 39 years old.

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While his political stances aligned closely with Markey's, Kennedy was seen as a favorite when he made his surprise announcement last September that he would leave the House of Representatives after eight years and try to stop fellow Democrat Markey's nomination to run in the Nov 3 election.

But Markey, who has been at the forefront of liberal causes ranging from stopping nuclear weapons proliferation to imposing strict new carbon emissions standards to curb climate change, mounted an aggressive campaign that was bolstered by progressive stars such as fellow Massachusetts Senator Elizabeth Warren and Representative Alexandria Ocasio-Cortez.

In his victory speech, Markey emphasized the urgency of tackling climate change after years of sputtering legislation.

"There will be no peace, no justice, no prosperity unless we stop the march to climate destruction. This is a matter of life and death," Markey said.

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Last year, he and Ocasio-Cortez unveiled the "Green New Deal" calling for slashing carbon emissions blamed for climate change.

With Markey's deep legislative record after more than four decades in the House and Senate and no personal controversies, Kennedy had a difficult time convincing Massachusetts voters to dump the veteran lawmaker.

Since 2018, progressives running in other states have unseated some more moderate, veteran House Democrats.

Markey's primary win paves the way for his expected reelection in November against Republican Kevin O'Connor, The Hill reported.

The result marks the first loss by a Kennedy in a Massachusetts election, according to the report.