The Labour Wrexham MP Ian Lucas has said he will not stand in the next general election.
He said on Friday evening he had informed his constituency party of the decision for “personal and family reasons”.
Mr Lucas was elected in 2001 after predecessor John Marek became an assembly member.
He held onto the Wrexham seat in 2017 with a majority of 1,832 votes – making it a key target for the Conservatives.
In a letter to Labour colleagues, Mr Lucas said the job had been a “demanding responsibility”.
“I am 60 next year. I have been an MP since I was 40. I think the time is right for me to choose to follow a different path in the years to come,” he said.
He added: “Thank you all for your support and loyalty and I will continue to serve the people of Wrexham to the best of my ability until the next election comes.”