Dewhurst made the announcement Tuesday while attending the Republican National Convention in Tampa. His decision ends weeks of speculation about his political future since losing a July runoff to Ted Cruz in the race to replace U.S. Sen. Kay Bailey Hutchison.
Spokesman Matt Hirsch says the 67-year-old Dewhurst still feels "there's a lot of work left to be done."
Dewhurst has served as lieutenant governor since 2003, but another term is hardly assured. Land Commissioner Jerry Patterson and Agriculture Commissioner Todd Staples have indicated they'll run to replace Dewhurst in two years.
The Texas lieutenant governor presides over the state Senate and wields considerable influence over state policy.