"Although I understand that I served at the pleasure of the president, I was nevertheless incredulous that the US government chose to remove an ambassador based, as best as I can tell, on unfounded and false claims by people with clearly questionable motives", Yovanovitch testified.
And she said Mr Trump had pressured officials to remove her for nearly a year.
Yovanovitch, who was recalled from her post in May after coming under attack from Trump's personal lawyer Rudy Giuliani and other conservatives with unsubstantiated allegations that she tried to hold up anti-corruption efforts in the Ukraine, is still a member of the foreign service. She said she had not spoken to Hunter Biden and had only spoken to Joe Biden several times over the course of many years in government. "She's a courageous woman", said Rep. Mike Quigley.
Trump was asked about the matter a day after two Giuliani associates were indicted in federal court on alleged campaign finance violations. Sessions declined to identify who informed him about her disparaging language.
Blitzer asked about concerns that Yovanovitch could face some sort of retribution for testifying after the State Department directed her not to appear.
A day earlier, USA prosecutors arrested two Florida businessmen tied to Giuliani, charging them with campaign finance violations.
Mr Parnas sought the help of a USA congressman to get Mr Trump to remove Ms Yovanovitch, according to the indictment.
Previously, in a broader discussion in which White House officials were reportedly encouraging Ukraine to continue its work to eliminate corruption in the country's energy sector, Gordon Sondland, the United States ambassador to the European Union and one in charge of ties with Kiev, thundered that there were also "investigations that were dropped that need to be started up again", according to a U.S. official familiar with the matter.
"I don't want to be pulled into this because I understand that my words could impact the elections of the American people", he added. "That is not unusual for you to meet people who then become contributors".
Representative Michael Quigley, an Illinois Democrat who attended Yovanovitch's appearance, was circumspect when he stepped out of the secure conference room where she spoke: "No comment but she's a courageous woman". The Trump administration found her "insufficiently loyal to the President and not committed to carrying out his foreign policy", a USA official familiar with her dismissal previously told TIME.
The ambassador's first scheduled deposition earlier this week was blocked by the state department.
U.S. Ambassador to Ukraine Marie Yovanovitch, center, sits during her meeting with Ukrainian President Petro Poroshenko in Kyiv, Ukraine, March 6, 2019. "And I don't know if I recalled her or somebody recalled her, but I heard very, very bad things about her for a long period of time".
But within the diplomatic community, many remain outraged at the abrupt dismissal of the veteran diplomat following what they say is a political smear campaign.
Yovanivitch, who was sworn in as ambassador to Ukraine in August 2016, had served in ambassadorships under three administrations.
During a day-long media event at a food court in Ukraine, President Volodymyr Zelensky continued to try to shove considerable distance between himself and the political scandal now engulfing President Trump.
Democrats were hoping to determine if Yovanovitch's removal was related to a pressure campaign, or particularly, her unwillingness to take part.
Trump had said in August he was considering Sullivan for the envoy job.
During that conversation, Mr Trump described Ms Yovanovitch as "bad news", according to a rough transcript released by the White House. "If anything, she is no news".
The State Department apparently did not demand that she not appear, as it did earlier this week with U.S. Ambassador to the European Union Gordon Sondland.
Yovanovitch defied a state department instruction not to speak to congressional committees leading impeachment proceedings against Donald Trump. The former mayor also provided information to both Trump and the State Department about Yovanovitch, who he suggested was biased against the president.