Popular Democratic Gov. John Lynch will not seek an unprecedented fifth term, NH Journal has learned from reliable sources. Lynch will announce his intention not to seek reelection on Thursday.

Sources tell NH Journal that Lynch has personally invited state commissioners and close political friends to a private lunch after the announcement. He will thank them for their hard work and honor their collective achievements.

Lynch’s announcement is expected to kick off a flurry of political activity and some interesting partisan jockeying. “This will only be the fourth time in twenty years that we’ll have an open seat in the governor’s race,” one source told us. “Expect a lot of people to jump into this thing.”

Former-State Senator Maggie Hassan (D-Exeter) is the favorite of liberal Democratic establishment and is expected to jump into the race quickly. As is Ovide Lamontagne, the popular conservative former U.S. Senate candidate who is expected to be the frontrunner to replace Lynch, at least in the early stages of the race.

Another probable candidate, Kevin Smith is likely to compete for the Republican nomination. Smith, a former state representative and one-time adviser to Gov. Craig Benson, has achieved notable success as the head of Cornerstone Policy Research, a powerful think tank and political advocacy group.

Other possible Republican candidates include State Senator Jeb Bradley, Manchester Mayor Ted Gatsas and 2010 Republican nominee for Governor John Stephen.

An NH Journal poll taken in January showed Lamontagne with a significant lead over some possible candidates.

There is little doubt Lynch would have been successfully reelected had he decided to run. An NH Journal poll from May showed Lynch with a 56% – 35% lead over Lamontagne.

UPDATE: WMUR’s James Pindell has more.