OTTAWA – Nathan Cullen, one of the NDP's best known and most effective MPs, is calling it quits.

The northern British Columbia MP announced Friday that he won't seek re-election this fall.

That makes 13 of the 44 New Democrats elected in 2015 — including five of the 14 in B.C. — who won't be running again.

Cullen's departure is a blow to NDP Leader Jagmeet Singh, who just won his own seat in the House of Commons in a B.C. byelection earlier this week.

Had Singh lost the byelection, Cullen would have come under heavy pressure to run for leader.

Cullen has represented the northern B.C. riding of Skeena-Bulkley Valley since 2004.

His announcement comes just 24 hours after another respected B.C. New Democrat — Victoria's Murray Rankin — announced he won't seek re-election. Another B.C. MP, Fin Donnelly, has also said he won't run again.

Two other New Democrat MPs in the province have already resigned their seats — Kennedy Stewart, who is now Vancouver's mayor, and Sheila Malcolmson, who is now an MLA. Former party leader Tom Mulcair also gave up his Montreal seat, which was captured by the Liberals in a byelection Monday.

Other New Democrats not seeking re-election include Quebec MPs Helene Laverdiere, Romeo Saganash, Anne Minh Thu Quach and Marjolaine Boutin-Sweet, Ontario MPs David Christopherson and Irene Mathyssen, and Alberta's lone NDP MP, Linda Duncan.

Cullen was considered a long-shot when he ran for the party leadership in 2012, but he wound up coming a respectable third. He declined to run again for the party's top job in 2017 after Mulcair was dumped.

The 46-year-old has young children and the travel between Ottawa and his remote, sprawling riding is gruelling.