Citing the White House's continued obstruction of oversight efforts by Congress, Ms Ocasio-Cortez said the US president's actions made such a move "entirely appropriate".
The influential Democratic congresswoman's intervention piles pressure on House speaker Nancy Pelosi, who has so far resisted calls for Democrats to launch impeachment proceedings.
Ms Pelosi instead backs continued investigations of Mr Trump and his administration by numerous congressional panels.
But more Democrats are openly discussing impeachment, and liberals like Ms Ocasio-Cortez, a leader of the progressive left since she beat an established Democrat in a surprise primary upset last year, are stepping up the pressure.
"I think it's time for us to, at the very least, open an impeachment inquiry ... we've been given no choice I think, in this scenario," Ms Ocasio-Cortez said outside the House of Representatives.
She said the Mueller report on Russian meddling in the 2016 campaign had described evidence of obstruction of the investigation by the executive branch, adding that the report had pointed directly to Congress as the body to take action.
The report by special counsel Robert Mueller stopped short of declaring the president obstructed justice, but it also refused to exonerate him.
"We now have the president actively discouraging witnesses from coming in to answer a legally binding subpoena from Congress," Ms Ocasio-Cortez added.
Former White House counsel Don McGahn on Tuesday defied a subpoena from the House judiciary committee, at the White House's request.
"It's getting to the point where we can't even do our own jobs. And I think it is entirely appropriate, given this overwhelming amount of evidence and the continued actions from the executive branch, that we exert our power as a co-equal branch of government," Ms Ocasio-Cortez said.
She said she was not sure whether impeachment advocates were a majority of the Democrats in the House, but "I personally have not felt a very strong opposition to impeachment".
Another Democratic politician, representative John Yarmuth, said on Tuesday he believed Ms Pelosi realises events were trending in the direction of impeachment, even as the Democratic leader argues for continued focus on House investigations of the Trump administration.
Ms Pelosi listened as advocates of impeachment spoke at a Monday night meeting with senior Democrats, Mr Yarmuth said.
"I think she realises that the path is leading more and more inevitably toward an impeachment process. But she wants to let all these committees do their thing," Mr Yarmuth said outside the House.
Additional reporting by Reuters