Councillor David Alderdice has submitted his resignation from North Down Borough Council.
Mr Alderdice announced his intention to stand down at last week's monthly council meeting, citing “professional commitments within the NHS”, where his workload has increased “considerably” over the past year.
The Alliance member said he was standing down reluctantly from the council but said it had been a “pleasure” to represent the people of Holywood.
Councillor Alderdice served 13 years in Local Government with eight years in Belfast City Council and five years in North Down Borough Council.
He was Lord Mayor of Belfast from 1998-1999, and during this time was awarded an OBE for Public Service.
Councillor Alderdice's resignation will come into effect at the end of this month. Vacancies may now be filled by party nomination or substitution.
This applies to all vacancies arising on or after April 1, 2010.