The premiership player and State of Origin representative, who joined the Bulldogs for the 2003 season, said it was “mentally and physically time” to call it a day.
Ryan has played 213 first-grade games for the Bulldogs after joining from Parramatta.
He said the 2004 premiership win was the highlight of his distinguished career.
A bustling, hard-running second rower, Ryan has scored 67 tries for the Bulldogs as he looks to lead the club to another finals series.
“Hopefully we can give it a good shake over the next five games and see what happens,” he said.