Pierre Zakrzewski, 55, and Oleksandra Kuvshinova, 24, were killed when their vehicle was struck by incoming fire in Horenka, on the outskirts of Kyiv.
Their colleague, Benjamin Hall, 39, was wounded in the incident and remains in hospital.
Fox News CEO Suzanne Scott said it was a "heartbreaking day" for the organisation.
Ms Scott said Zakrzewski's "passion and talent as a journalist were unmatched".
"Pierre was a war zone photographer who covered nearly every international story for Fox News from Iraq to Afghanistan to Syria during his long tenure with us," she said.
Senior field producer for Fox Yonat Friling said Kuvshinova had been working with the team for the past month and "did a brilliant job".
"We have lost a beautiful brave woman" Ms Friling said. "She loved music and she was funny and kind."
Irish Prime Minister Micheál Martin said he was "deeply disturbed" by the killing of Kuvshinova and Zakrzewski, who was an Irish citizen.
"My thoughts are with their families, friends and fellow journalists," the taoiseach tweeted.
News that Mr Hall was injured emerged on Monday but Ms Scott gave no further detail.
On Monday Anton Gerashchenko, an adviser to Ukraine's interior minister, posted on Telegram that Mr Hall was in a serious condition.
Mr Hall joined Fox News in 2015 and has been heavily involved in the network's foreign affairs coverage.
He has covered several wars from the frontlines, including in parts of the Middle East.
A dual US-UK citizen, he completed both his undergraduate and graduate degrees in London.
The attack which killed Zakrzewski and Kuvshinova follows the death on Sunday of 50-year-old US journalist Brent Renaud, who was shot and killed in the town of Irpin.
According to Lyudmyla Denisova, the Ukrainian parliament's human rights chief, at least two other Ukrainian journalists have also been killed.
