Sondland said the president's lawyer, Rudy Giuliani, demanded that Ukrainian president Volodymyr Zelensky make public statements that he was opening investigations into a company linked to Democratic presidential candidate Joe Biden's son, and into a discredited theory that Ukraine interfered in the 2016 U.S. election.
"Mr. Giuliani's requests were a quid pro quo for arranging a White House visit for President Zelensky," Sondland said.
Sondland said he and Giuliani were working at the president's "express direction." "We did not want to involve Mr. Giuliani," he said.
He said he was later dismayed to learn that U.S. military aid to Ukraine had been suspended pending Ukraine launching the requested political investigations.
Donald Trump has denied pressuring Ukraine and said there was no quid pro quo.