Brown, 56, secured the backing of enough Labour MPs to ensure he will not face a contest to become the next Labour leader and Prime Minister.
The Chancellor got an overwhelming 308 nominations fromthe 353 MPs while McDonnell was 16 nominations short of the 45 required. Brown should now take over unopposed after Blair steps down on June 27.
"With Gordon Brown having gained 308 nominations from Labour MPs, it is now mathematically impossible for me to reach the nominations to stand," McDonnell conceded last night, expressing disappointment on behalf of Labour Party members and it was a "blow to democracy".
"Naturally I congratulate Gordon and wish him every success, but it is a great shame that Labour Party members will not be allowed a vote on the party's future direction,"he said.
Even bitter rivals of Brown - including former HealthSecretary Alan Milburn - endorsed him. Today was the last day for filing nominations. Candidates who get 45 or more nominations go to a ballot of party members, trade unionists, Labour MPs and European Parliament members.
"We are delighted that the party is united behind Gordon and giving him such overwhelming support," said Brown's campaign leader Jack Straw.
The Chancellor will have to wait until June 24 to be declared party leader at a special conference in Manchester. He will become Prime Minister three days later on June 27 after Blair visits Buckingham Palace to offer his resignation to the Queen. Minutes later, Brown will be ferried from No 11 Downing Street in a Prime Ministerial armour-plated Daimler for the first time to get the seal of office from the Queen. He will then return to Downing Street - and move into No. 10 as the 52nd Prime Minister of Britain.
Deputy leader John Prescottt also steps down on June 27. There are six contestants for his post, of whom one, International Development Secretary Hilary Benn - with 42 officially listed nominations is yet to get through to the national ballot. Backbencher Jon Cruddas, Education Secretary Alan Johnson, Justice Minister Harriet Harman, Northern Ireland Secretary Peter Hain and Labour chairman Hazel Blears have all got through.
Those candidates who make it to ballot paper will take part in 10 hustings around the country ahead of the special conference in Manchester, when the new leader and deputy leader will be named.