The announcement that Mr Sawyer was to step down after four years and the likelihood that he will be replaced by his deputy, Margaret McDonagh, mark another symbolic step for the new Labour hierarchy.
Although Mr Sawyer has been a loyal general secretary, he came from a trade union background and was at one stage regarded as left-wing.
Ms McDonagh, who is 36, is seen as new Labour to the core even though she was at one time a researcher for the electricians' union.
In a statement yesterday Mr Sawyer said that the party needed a new generation of officials to win a second term for Labour. It is thought likely that Mr Sawyer will be made a life peer.
He said he had made it clear when he became general secretary that he would resign after the general election.
He added: "I have helped with the transition from opposition to government, moved our headquarters to Millbank and introduced a new management structure for the party. This is the right time for me to move on."
Mr Sawyer will place his resignation before the party's National Executive Committee at its meeting on 26 May.
A former trade union leader, he became general secretary in 1994 at Tony Blair's request. Last night Mr Blair described him as "one of the finest general secretaries in the party's history. He has been a loyal colleague and friend. I shall miss his advice and judgement, but I know he will put his considerable skills and qualities to good use in other roles for many years to come."
Mr Sawyer, 54, came to Labour Party politics through the trade union movement. He joined in 1968 after beginning his working life as an apprentice engineer in Darlington. Later he became a full-time organiser with the public sector union Nupe, then moving to London as deputy general secretary under Rodney Bickerstaffe.
In 1987, he became chairman of Labour's home policy committee, and by 1990 was chairman of the party. He was involved in the expulsion of Militant from Labour and supported John Smith's highly controversial reforms on one-member one-vote.
Mr Sawyer still has six months' notice to work out. Labour Party officials expect him to stay in post until after this year's annual conference in Blackpool.