Gerretsen, the member for Kingston and the Islands, made the announcement Friday afternoon outside his Kingston constituency office.
He said he wanted to give the next Liberal candidate adequate time to prepare for an election.
The next provincial vote is scheduled for 2015, but it could happen sooner as the Liberals have a minority government.
Gerretsen's political career started in the early 1970's, when he was elected as a local alderman.
He served as mayor of Kingston from 1980 to 1988.
He was first elected as the member of the legislature for Kingston and the Islands in 1995 and held a number of cabinet portfolios before being appointed attorney general in October 2011.