The Londoner arrived at Prenton Park from Gillingham in July 2007 and played a key role as Tranmere missed out on the play-offs on the final day of the season.
Chorley told Tranmere's official website: "I really enjoyed my time at Tranmere. I was settled, I had a baby and my family were up here. I was just disappointed we missed out on the play-offs at the last minute.
"Once the season was over I spoke to my family and we discussed my options. Fortunately there were a number of clubs interested, a few of them from down south, and I decided to move to Leyton Orient for a number of reasons.
"They offered me the best deal and for football reasons. Going back
down south was also part of my decision, though I liked living in Merseyside. I've still got my flat in Liverpool and I felt like I was an adopted scouser during my time there.
"I'd like to thank the Tranmere fans. They were brilliant with me, especially in my second season at the club. I'm just disappointed they didn't get to see us in the play-offs."