The prime minister paid tribute to a "remarkable man" after Boris Yeltsin died yesterday.
Tony Blair said he was "very saddened" to hear of the death of Mr Yeltsin. The former Russian president died of heart failure at the age of 76.
Describing him as a "remarkable man", Mr Blair joined with world leaders in praising Mr Yeltsin's "vital role" in Russian history.
In a statement, Mr Blair said: "I was very saddened to learn of the death of former President Yeltsin.
"He was a remarkable man who saw the need for democratic and economic reform and in defending that reform he played a vital role at a crucial time in Russia's history."
The Foreign secretary Margaret Beckett extended her sympathy to Mr Yeltsin's family, while crediting the former president with transforming relations between Russia and the West.
"Boris Yeltsin contributed to setting Russia on the path of reform, especially in facing down the coup attempt of 1991," she said.
Former prime minister Sir John Major also spoke of Mr Yeltsin's role in democratising Russia.
Mr Yeltsin became Russia's first elected president in 1991, before resigning on New Year's Eve 1999.
Shadow foreign secretary William Hague said Mr Yeltsin would always be associated with the creation of democracy in Russia and would be remembered as the man who led his country through a "turbulent transformation in far calmer fashion than many had feared."
Despite this, Mr Yeltsin was often criticised during his lifetime for paving the way for wealth oligarchs and alleged corruption in capitalist Russia. He was also mocked for his heavy drinking and often erratic behaviour.
Nevertheless, former British foreign secretary Sir Malcolm Rifkind said Mr Yeltsin succeeded in preventing the Communists regaining control after a failed coup against Mikhail Gorbachev in 1991.
Mr Yeltsin's body is to lie in state in Moscow before he is buried on Wednesday. The day has been declared a national day of mourning.