Rendell, a Democrat whose two terms as governor ended in January 2011, was a character witness for Stetler on the fifth day of his trial in Dauphin County court. He noted the several dozen people who nearly filled the seats on Stetler's side of the courtroom as a reflection of strong community support for him.
"I took a 6:25 train up here this morning and I'm on my way back" to Philadelphia, Rendell told reporters after his brief testimony. "There are very few people I would take a 6:25 train for."
Rendell was the first in a long procession of character witnesses who testified Monday.
Later in the day, lawyers for the prosecution and defense made their closing arguments, and Judge Todd Hoover instructed the jury on the law. Jurors planned to begin deliberations on Tuesday.
Stetler, 62, served as a state representative from York County for 16 years. The corruption charges against him involve the period between 2004 and 2006, when he was chairman of both the House Democratic Policy Committee and the House Democratic Campaign Committee.
He has pleaded not guilty to four counts of theft and one count each of conspiracy and conflict of interest.
Some of his former employees who testified for the prosecution said they routinely did campaign work on state time, including opposition research to expose the weaknesses of Democrats' political opponents. Stetler, testifying on his own behalf last week, denied the allegations and insisted that he instructed his employees "face to face" to keep public and political business separate.
Rendell, a former Philadelphia mayor and district attorney who was invited to testify by Stetler's daughter, said Stetler never should have been charged.
"I think that this prosecution was a mistake," he told reporters, citing "fairly clear" evidence that Stetler did not break the law. But he acknowledged that, "I'm not here to be a fact witness."
Stetler served as state revenue secretary under Rendell for about 11 months until he resigned just hours before he was charged in 2009.
He was among the last of 25 former legislators and ex-aides who were charged in what the state attorney's office says is an ongoing investigation of government corruption.
Twelve Democrats and nine Republicans have been convicted or pleaded guilty. Two defendants were acquitted, and charges against a third were dropped.