Dave Watts, who has represented St Helens in Parliament for the past 17 years, is to step down from frontline politics at the next election.
He told local party members of his decision - which ends months of speculation about his future - during a series of meetings over the weekend.
It brings to an end a political career as an elected representative stretching back to his election as a local councillor in 1980.
Mr Watts, who will turn 64 in August, said he feared he would be unable to maintain the same level of commitment to the job if he sought re-election.
He cited his role in securing funding for St Helens College, schools and hospitals as well as helping deliver the Blackbrook by-pass as the major achievements of his Westminster career.
“I am also proud of the role that I played in securing planning permission and government funding for our new Saints stadium,” he added.
“I very much enjoyed helping Eamonn McManus realise his vision for the club.
“I am very grateful for the support of my party, especially my party officers; Alan Cunliffe, Andy Bowden, Keith Roberts, Linda Maloney and Janet Richardson who have always given me their full support over the years.”
Mr Watts also thanked council leaders and business leaders for their support.
Labour leader Ed Miliband was one of the first to pay tribute to Mr Watts, who will also step down as chair of the Parliamentary Labour Party.
He said: “Dave Watts has been a fantastic member of parliament for St Helens North and we will miss him very much.
“Since being elected chair of the Parliamentary Labour Party in 2012 Dave has led the parliamentary Labour party with his trademark good humour, diligence and decency.
“Respected and well liked across the whole party Dave will leave a big hole.
“I want to thank him on behalf of the whole Labour movement and on a personal level for the kindness, friendship and loyalty he has always shown me.”