Yovanovitch, who was abruptly recalled from Ukraine in May, is scheduled to give a deposition to House investigators probing Trump in a scandal that has cast a pall over his presidency. She did not respond to questions posed by reporters.
The Democratic lawmakers leading the inquiry were waiting to see if Yovanovitch showed up after the White House said earlier in the week it would refuse to cooperate with an inquiry that the Republican president has termed "a kangaroo court."
A career diplomat who has served as U.S. ambassador to two other countries, Yovanovitch's stint as ambassador in Kiev was cut short when she was recalled to Washington in May as Trump allies leveled unsubstantiated charges of disloyalty and other allegations against her.
According to media reports, Trump took the action after complaints by his personal lawyer Rudy Giuliani and others that she had obstructed Giuliani's efforts to persuade Ukraine to investigate Biden. Democrats have called her removal politically motivated.
Gordon Sondland, the U.S. ambassador to the European Union, will comply with a House subpoena and testify next Thursday before the committees leading the impeachment inquiry, his lawyers said.
But Sondland is not authorized to release the documents the House committees have sought, his lawyers said, adding that he hopes the material will be shared with the committees before his appearance. Sondland was initially scheduled to testify before the House committees on Tuesday, but was blocked by the Trump administration from appearing.
Sondland, a Trump political donor who contributed $1 million to the Republican president's inauguration committee, exchanged text messages about Washington's relationship with Ukraine with other top diplomats. House Democrats received a cache of the texts as part of their impeachment inquiry.
Sondland was a Seattle-based hotelier until Trump nominated him to his position as ambassador in May. He was confirmed by the U.S. Senate in June and presented his credentials at the European Commission in July.
The inquiry was launched after a whistleblower complaint from a person within the U.S. intelligence community about a July 25 phone call, in which Trump pressed Ukrainian President Volodymyr Zelenskiy to investigate a domestic political rival, Joe Biden, and Biden's son Hunter Biden.
Biden, the former U.S. vice president, is a leading Democratic contender for the right to face Trump in the November 2020 presidential election.
Democrats have accused Trump of pressuring a vulnerable foreign ally to dig up dirt on a domestic opponent for his own political benefit. Trump has denied he did anything wrong on the call.