Ukrainian-American businessman Lev Parnass, who is facing separate criminal charges, made the comments in an interview with MSNBC on Wednesday after letters, phone records, notes and flash drives were obtained from him earlier this week, the BBC said in a report.
Documents show that the Ukraine-born Parnas was in regular contact with Giuliani as well as Ukrainian officials, and suggests that the businessman was directly involved in trying to have Ukraine's President Volodymyr Zelensky look into the Bidens.
In the interview, Parnas said Trump was "aware of all my movements".
"I wouldn't do anything without the consent of Rudy Giuliani or the President. Why would President Zelensky's inner circle or (Interior) Minister (Arsen) Avakov or all these people or (former) President (Petro) Poroshenko meet with me?
"Who am I? They were told to meet with me. And that's the secret that they're trying to keep. I was on the ground doing their work," he added.
Parnas further said that the President was lying and knew that unless there was an investigation into Joe Biden and his son Hunter, who was a director of a Ukrainian gas company, military aid to Kiev would be withheld.
He also claimed that the investigation was about digging up dirt on Joe Biden.
Meanwhile, some of the materials obtained show Parnas and Giuliani discussing the removal of Marie Yovanovitch, the then US ambassador to Ukraine, said the BBC report.
In Wednesday's interview, Parnas claimed the only motivation to get Yovanovitch removed from her post was because she was in the way of the effort to get Ukraine to announce an investigation into Joe Biden.
Trump was impeached by the Democrat-controlled US House of Representatives on December 18, 2019 and is accused of abuse of power and obstruction of Congress.
The two articles of impeachment were sent to the Republican-majority Senate on Wednesday night, paving the way for the starting of a trial against the President.
( With inputs from IANS )