The Art Fund, which currently distributes £4.5m annually, will increase its funding to £7m a year.
It said the move was in response "to the severe financial pressures facing most institutions".
The charity has given more than £24m to 248 museums over the past five years through grants and fundraising.
The Art Fund also announced its plans to develop and expand its funding programme.
It said it would run more public fundraising campaigns to save art at risk of being lost from UK collections, such as its recent £6m Brueghel and Staffordshire Hoard campaigns.
The charity has also formed a new partnership with the National Gallery to offer funded curatorial traineeships in two regional museums.
Tate director Nicholas Serota said: "I applaud the bold commitment of the Art Fund at a time when so many funding bodies are reducing their support for museums.
"If our museums are to thrive, we must continue to grow and develop our collections."
The Art Fund also relaunched its membership card - which will now be known as the National Art Pass - offering free or discount admission to more than 200 museums and galleries.
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