After being taken to Surfers Paradise Station, officers discovered a small bag of cocaine in one of his pockets while conducting a search.
In a tearful apology the next day, Walsh admitted he had used the drug during the night.
"This is solely on me. I should never have done it. It's a mistake that I've made and I'm aware of that. I'm remorseful and should never have done it," he said at the time.
On Monday he pleaded guilty to charges of cocaine possession and contravening a move-on order.
He was fined $400 and placed on a $500 good behaviour bond by Magistrate Ron Kilner. No conviction was recorded.
He was earlier this month fined $5000 by the NRL and handed a two-game ban for the start of next year.
Outside court on Monday, Walsh again expressed his remorse and said he hoped he had turned a page.
"I'm just really embarrassed and ashamed of what happened," he said outside court.
"I'm going to repay my family, friends, the club, the fans.
"Put all this stuff behind me; I'm going to work really hard to bounce back."