Richard Desmond, whose publishing company owns the Daily and Sunday Express, has donated £1m to UKIP.
Mr Desmond said UKIP was “not run by elitists” and was a party for “good, ordinary British people”.
UKIP leader Nigel Farage said the money would help “significantly” in its fight “against the big battalions”.
Mr Desmond, owner of Northern and Shell Media Group, donated £300,000 to the party late last year.
As well as the Daily and Sunday Express, the group publishes OK! and Now! magazines, as well as the Daily Star and Daily Star Sunday.
Mr Desmond said UKIP, which campaigns for the UK’s exit from the European Union, did not have “a massive party machine or highly paid public relations people” and was “struggling to have a voice”.
Explaining his donation on the Express website, Mr Desmond said: “They are human; they are not perfect and they do not pretend to be. But what they believe in is the best for the British people.
“They are the sort of people who will stand up for people who are struggling.”
Mr Desmond donated £100,000 to the Labour Party in 2001, around the time of Northern and Shell’s takeover of the Express.