Andrew Austin (Labour), who represented the Trinity Ward, has now ceased to be a town councillor after being given written notice of the situation by the Town Clerk.
Mr Austin was elected to the role in a by-election in April 2013, following the resignation of Mrs Gill Burton.
Mr Austin stood for re-election in the local elections last May, and was elected unopposed alongside Labour colleague Coun Ros Jackson.
The third and final seat in Trinity Ward was filled by Coun Sue Crew, who was co-opted on to the Town Council in June 2015.
Mr Austin told the Leader: “I’m sad to leave Louth Town Council, but with a new full time job and supervising after school clubs, coupled with four children at home, I struggled to maintain my commitment to my ward.
“I have worked alongside some of the most committed and selfless people both within the Labour Party and amongst my Independent and Conservative Party colleagues.
“No matter what our disagreements, I know that they all have the best interest of the amazing town of Louth at their heart.
“I wish whoever becomes the new councillor for Trinity Ward nothing but success.”
The Mayor and ELDC Elections Officer have been notified of the situation, and the vacancy will be subject to formal notices issued by ELDC to inform electors and to receive requests for an election. If there are no such requests, the vacancy will be filled by co-option.