Crowley, a 10-term Democrat, had possible ambitions to challenge Minority Leader Nancy Pelosi for House speaker if Democrats were to take a House majority in November's mid-term elections.
Ocasio-Cortez, a former Bernie Sanders volunteer from a Puerto Rican family, won with a 57.5 per cent majority on Tuesday. Crowley, who had not faced a challenger from his own party in 14 years, had 42.5 per cent in the majority ethnic minority district, the US media reported.
The political novice, who describes herself as a socialist Democrat, had huge grassroots support and raised more small-dollar donations than any other New York City congressional candidate.
"This is not an end, this is the beginning. This is the beginning because the message that we sent the world tonight is that it's not OK to put donors before your community," Ocasio-Cortez said while adressing her roaring supporters.
Ocasio-Cortez will now face Republican candidate Anthony Pappas in the November mid-terms. If she wins, she will become the youngest ever woman elected to Congress.
She promoted proposals such as Medicare for all, a jobs guarantee and abolishing Immigration and Customs Enforcement.
During her campaign, she criticised Crowley on his ties to Wall Street and accused the "56-year-old white man" of being out of touch with his increasingly diverse constituents, CNN reported.
After the result, both Ocasio-Cortez and Crowley thanked each other, with the latter saying he would support her in the mid-terms.
In a statement, Pelosi congratulated Ocasio-Cortez on her victory. The California Democrat said Crowley brought "principled, unifying and forward-looking leadership to the historic challenges of the Trump administration".
President Donald Trump, for his part, cheered Crowley's loss. In a tweet Tuesday night, he called Crowley a "Big Trump Hater" and suggested the representative would have done better if he had supported the President more often.
"Perhaps he should have been nicer and more respectful to his President!" Trump wrote.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
