The co-author of the gay-themed group's thumping hits "In the Navy" and "YMCA," Willis was arrested in March on drug and gun charges. The arrest marked the latest in a series of troubles the musician has had with the law since leaving the band in 1980.
In a plea deal, he did not contest one count of drug charges and two other counts were dropped. He is scheduled to be sentenced on September 1 and faces a possible prison sentence.
Willis was arrested last year on charges of possessing a gun and cocaine, but he disappeared after agreeing to a plea deal. Now he remains behind bars pending sentencing.