This comes just after the House Intelligence Committee wrapped up five days of public testimony in the impeachment inquiry.
"This was not an angel, this woman, okay?" Trump said, speaking of Yovanovitch. "I just want to let you know, this was not a baby that we’re dealing with."
He has also made unfounded allegations that Yovanovitch refused to hang up his portrait at the U.S. Embassy in Kyiv, Ukraine.
This wasn't the first time Trump has spoken harshly of the ambassador. On Nov. 15, even as Yovanovitch was testifying publicly, Trump tweeted: "Everywhere Marie Yovanovitch went turned bad."
House Democrats have since accused Trump of witness intimidation -- an accusation they said might be considered for potential articles of impeachment. During her hearing, Yovanovitch said she found Trump’s tweets "very intimidating."
Trump told the "Fox and Friends" co-hosts that he'd heard bad things about her.
"But this ambassador, that you know, everybody says is so wonderful, she wouldn’t hang my picture in the embassy, okay?" he said, without offering any evidence, claiming it was standard procedure for ambassadors to hang pictures of the president in the U.S. embassies.
"She’s in charge of the embassy, she wouldn’t hang it. It took like a year and a half, or two years for her to get the picture up," Trump said.
Yovanovitch’s team pushed back after Trump's interview aired, saying it was impossible to hang those photos because official federal photos had not arrived until nearly nine months after Trump’s inauguration.
ABC News confirmed with State Department officials that the federal government did not send official portraits out to federal offices and embassies until many months after Trump went into office. It was already 2018 when the pictures of Trump, Vice President Mike Pence and former Secretary of State Rex Tillerson were hung, according to State Department officials.
Lewis Lukens, the former top U.S. diplomat in the United Kingdom, wrote on Twitter that it took the White House almost 15 months to send out official photos.
"The Embassy in Kyiv hung the official photographs of the President, Vice President, and Secretary of State as soon as they arrived from Washington, D.C.," Yovanovitch’s lawyer told ABC News.
House Republicans never questioned her about the portraits either during her public testimony or in her nine hour closed-door testimony.
"She said bad things about me," Trump said. "She wouldn’t defend me. And I have the right to change an ambassador."
Yovanovitch did not explicitly say negative comments about the president in either her public testimony or private deposition. She said during her testimony that when she was advised by EU Ambassador Gordon Sondland to send a tweet praising Trump, she choose not to because she said "it felt partisan, it felt political." She said she didn't feel it would help "in keeping with my role as ambassador and a Foreign Service officer."
Despite widespread criticism, Trump continued to defend his attacks against Yovanovitch.
"There are a lot of things that she did that I didn’t like," he said.
During impeachment inquiry proceedings, House Republicans used the same argument.
"The president of the United States is the chief person in charge of policy and the executive branch," New York Rep. Lee Zeldin told ABC News, backing up the president’s right to control foreign policy and choose ambassadorships.
While the public impeachment hearings are finished for now, Yovanovitch is still an employee at the State Department, serving under Secretary of State Mike Pompeo.
ABC News' Katherine Faulders and Conor Finnegan contributed to this report.