(Reuters) - Rudy Giuliani, Donald Trump's onetime personal lawyer, arrived at an Atlanta courthouse on Wednesday to testify in a Georgia criminal probe examining attempts by the former U.S. president and his allies to overturn the 2020 election results.

Giuliani, who helped lead Trump's election challenges, was due to testify before a special grand jury in Fulton County after a judge ordered him to comply with a subpoena. His lawyers say he will refuse to answer questions that violate attorney-client privilege.

The former New York City mayor, 78, appeared before Georgia state lawmakers in December 2020, echoing Trump's false conspiracy theories about stolen ballots and urging them not to certify Democratic President Joe Biden's victory over the Republican Trump.

"It's a grand jury and grand juries, as I recall, are secret," Giuliani told CNN on his arrival at the courthouse, when asked to comment on his testimony. "They ask the questions and we'll see."

The Fulton County probe began after a January 2021 recorded phone call in which Trump urged the state's top election official to "find" enough votes to alter the outcome. The former president has asserted falsely that he won Georgia, as well as the 2020 presidential contest.

The special grand jury was convened in May at the request of county District Attorney Fani Willis.

Giuliani, a former crime-fighting U.S. Attorney, was among several Trump advisers and lawyers who received subpoenas from the grand jury last month, including Senator Lindsey Graham (R-SC).

(Reporting by Rami Ayyub, editing by Ross Colvin and Howard Goller)