"This is one of several large donations I have made to political and other causes. I'm proud to be a long-standing supporter of the Labour party and the Labour government.
Lord Hamlyn made the disclosure himself after growing pressure on Labour for details of the gift to be made public.
In a statement he said: "Having followed the debate on donations to the Labour party for the past few days, I'm happy to make public that I recently made a £2m donation to the party.
"This is one of several large donations I have made to political and other causes. I'm proud to be a long-standing supporter of the Labour party and the Labour government.
"Under the existing legislation I'm under no obligation to disclose the sum I have donated but I'm happy to do so."
The move comes shortly before new rules come into effect, introduced by the government, that force political parties to identify all donors giving more than £5,000.
Lord Hamlyn said he had given the money under the old rules but had not wished for publicity because he was recovering from a serious illness.
He insisted he would make "no apologies" for supporting the Labour party.
Party support
Labour party chairwoman Maggie Jones said: "Paul Hamlyn is a respected businessman and a well-known supporter of the Labour party.
"The party is proud of the fact that people like him support us and that we are able to attract substantial donations from business people."
She said Labour had recently received a number of "substantial donations" and it would be "quite wrong" for it alone to apply the new disclosure rules retrospectively.
Lord Hamlyn was made a CBE in 1993 by the Conservative government for charitable services.
The peer heads the Paul Hamlyn Foundation which makes donations to the arts and educational causes.
He is listed as giving in excess of £5,000 to Labour in each of the last four years. He was given a peerage in 1998.
Generous giver
Restaurateur and designer Sir Terence Conran, a friend of Lord Hamlyn for 30 years, told BBC Radio 4's World at One: "I don't think he necessarily sought to disguise his gifts but he doesn't brag about them".
"He's been an extremely generous giver to many good causes and obviously he sees the Labour party as one of them.
Sir Terence added that his friend had been "very ill for a very long time".
"I have never known anybody so heroically battle with illness - it has gone on and on and on and on and he never loses his determination to get through it all," he said.
Party concern
As well as criticism from Tories over the affair, Labour faced internal pressure to name the donor from parliamentary party chairman Clive Soley, former defence minister Peter Kilfoyle and MP Glenda Jackson.
Cabinet Office Minister Lord Falconer told the BBC he was "glad" Lord Hamlyn had come forward but stressed it was this government that had brought in the new rules.
BBC political editor Andrew Marr said the identity of the donor, which had been the subject of widespread speculation, was not a surprise.
It had "looked awful", he added, for Labour to try and keep his identity secret just before the Political Parties Elections and Referendums Act became law.