Towhey - who was named Perzel's chief of staff in 2007 as the probe led by then-Attorney General Tom Corbett was under way - could face a maximum prison sentence of five years on each count and total fines of $20,000.
Samuel "Buzz" Stokes, 69, of Philadelphia, Perzel's brother-in-law and former campaign manager, and former campaign aide Don McClintock, 43, of Voorhees, took similar pleas on Wednesday.
In court on Friday, Senior Deputy Attorney General Kenneth Brown said that between 2003 and 2007, Towhey conspired with others, including the once-powerful Perzel, to use public money for campaign purposes.
Sentencing will most likely take place after the trial, said Nils Frederiksen, a spokesman for Attorney General Linda Kelly.
Towhey and his attorney, Timothy Woodward, declined to comment.
Frederiksen said no other pleas were scheduled before jury selection for the remaining seven defendants, which is scheduled to begin Sept. 6.
Perzel, who represented Northeast Philadelphia for 32 years until he was defeated in November, has maintained his innocence and said he had no intention of taking a plea.
Prosecutors allege that Perzel and the other defendants, including another former lawmaker, Brett Feese of Lycoming County, used as much as $10 million in taxpayer money to fund campaign activities.
Among the charges: using the House Republican information-services office to develop computer software programs that targeted political opponents, including Republican lawmakers who had not voted as Perzel directed, according to the grand jury report.
Towhey was originally charged with 26 counts that also included theft, hindering apprehension, and obstruction of justice. Prosecutors said he and other GOP officials hid boxes of campaign material from the Attorney General's Office.
The Bonusgate probe also led eventually to the arrests of 15 current and former Democratic legislators and aides, including three who were convicted at trial, two who were acquitted, and seven who pleaded guilty.
Contact staff writer Amy Worden at 717-783-2584 or aworden@phillynews.com.