The addition of Mr. Holmes to the witness list follows a closed-door deposition he gave Friday describing a cellphone conversation he listened to in July. While sitting on the outdoor patio of a restaurant in Kyiv, the Ukrainian capital also known as Kiev, Mr. Holmes said he heard the president ask Gordon D. Sondland, the ambassador to the European Union, if President Volodymyr Zelensky of Ukraine would move forward with the investigations Mr. Trump sought.

Late Monday, the House Intelligence Committee released transcripts of the testimony of Mr. Holmes and David Hale, the under secretary of state for political affairs.

Mr. Holmes called the cellphone conversation he overheard in Kyiv between the president and Mr. Sondland “remarkable,” and he testified that it was clear to him that officials in Ukraine “gradually came to understand that they were being asked to do something in exchange for the meeting and the security assistance hold being lifted.” His account underscored that, contrary to Mr. Trump’s claim that Ukraine’s leaders never knew American aid was being withheld, top officials there were well aware that it was, and that they had to do what the president wanted before they could receive it.

Mr. Holmes gave a vivid account of the cellphone call between Mr. Trump and Mr. Sondland, and of a subsequent conversation in which the ambassador told Mr. Holmes that Mr. Trump did not care about Ukraine , only about “big things,” such as investigations of the Bidens.

“ There’s just so much about the call that was so remarkable that I remember it vividly,” Mr. Holmes said, according to the transcript. He said he recounted the conversation to his boss at the embassy after the lunch and said she was “shocked” by it. Mr. Holmes said that in morning embassy staff meetings, he would often refer back to the call as a way of trying to explain Mr. Trump’s reluctance to schedule a White House meeting with Mr. Zelensky.

“I would say, ‘Well, as we know, he doesn’t really care about Ukraine. He cares about some other things,’” Mr. Holmes testified.

Mr. Hale offered new details about deliberations within the State Department over the recall of Marie L. Yovanovitch as ambassador to Ukraine. By the end of March, he said the department was debating whether to issue a statement of support for her amid unrelenting attacks by Rudolph W. Giuliani, the president’s personal lawyer, and others.