Wanganui Mayor Annette Main said she received Michael Laws' resignation by email on Sunday afternoon and was pleased it was official, because they could start planning for his replacement.
Mr Laws, whose resignation will come into effect on May 1, is leaving Wanganui for a job in Timaru.
"He has made a decision to move for a position and to move his family. I respect that," said Ms Main.
"I understand that people's circumstances change, and they can change during the time they have been elected to council."
It was "unfortunate" Mr Laws was resigning, but the role of councillor required someone able to be in touch with what was happening in Wanganui.
She weighed the cost of a by-election against the cost of having a councillor unable to be present at meetings.
A by-election is expected to cost ratepayers $40,000.
Chairwoman of the Whanganui District Health Board, Dot McKinnon, said it was with regret she accepted Mr Laws' resignation from the board.
"Since his election to the board in October 2007, Mr Laws has been a skilled and effective lobbyist for Wanganui's health service," said Ms McKinnon.
"He's worked hard to ensure Wanganui retains the health services we've had to date.
"His efforts to improve our services for the elderly and to stabilise Wanganui District's maternity services have been particularly effective."
Mr Laws' replacement on the health board would be by ministerial appointment.
Mr Laws served as Wanganui mayor from 2004 to 2010 and was elected to the DHB in 2007 and re-elected in 2010.