James Rainford entered the plea during a court appearance in Van Nuys and was immediately sentenced. He was also ordered to stay away from Waits when he is released and was sentenced to three of informal probation.
Rainford was seen lunging and grabbing the back of the neck of Cy Waits as he and Hilton walked into a Van Nuys courthouse to testify against a man arrested outside the socialite's home in 2010.
Rainford was tackled by Hilton's security and turned over to police. He said he was not trying to attack her but only tried to approach her to autograph a photo of himself proposing to her.
Rainford had twice been arrested for showing up at Hilton's house and fighting her security guards, once in January and again in October.
Nathan Lee Parada of Redlands is accused of trying to break into Hilton's home last year. He's charged with a felony count of attempted residential burglary.
Jurors are due back in court Friday for deliberations in his trial.
The Associated Press and City News Service contributed to this report.