The outgoing president turned to Mr Giuliani after a string of courtroom defeats in battleground states across the US.
The move came after Arizona and Georgia were called for president-elect Joe Biden, giving the former vice president 306 electoral votes to Mr Trump’s 232.
Mr Giuliani’s new role comes just a week after he was widely mocked for his role in a bizarre press conference in front of Four Seasons Total Landscaping in Philadelphia.
And that came just weeks after Mr Giuliani was forced to deny he had acted inappropriately on camera in Sacha Baron Cohen’s sequel Borat movie.
But Mr Trump wanted to bring on “fighters” to help make his widely discredited case for voter fraud.
The president has suffered a series of legal defeats in Arizona, Pennsylvania and Michigan and has seen Mr Biden named by CNN and other media organisations as the winner of Georgia, which is doing a hand count audit of ballots.
The cyber-security section of the government’s Department of Homeland Security has also reported that the election was the “most secure in American history.”
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