The phrase "a significant supporter" is correct and usable in written English.
You can use it to describe someone who provides considerable help or backing to a cause, organization, or individual.
Example: "The charity was able to expand its programs thanks to a significant supporter who donated a large sum of money."
Alternatives: "a major backer" or "a key advocate".
As for Assange, he already has a significant supporter base.
Mr. Politi was also a significant supporter of the Edmundite Fathers and St. Michael's College in Colchester, VT.
Qatar has been a significant supporter of the Syrian rebels since the uprising began in March 2011.
Cameron has been a significant supporter of equal marriage, saying that he did not want sexuality to be a barrier to the support of marriage for all.
As well as being an influential figure in the arts world, Walsh is a significant supporter of charities and sporting and education organisations.
My business partner Vivian Lau (Harvard College '00), who is also a significant supporter of HLS's Environmental Law Program, and who worked closely with me at Goldman Sachs, reunited with me in 2008.
He remained a loyal and significant supporter of the organization and we were enriched by knowing him.
Mr. Adachi does not seem inclined to join Mr. Lee's effort, though, and Mr. Adachi's most significant supporter, Michael Moritz, a venture capitalist, was dismissive of the plan.
Not surprisingly, Glock is also a significant financial supporter of the National Rifle Association.
That has increased the confidence of Gordon Brown to propose this: significant supporter ownership in clubs – the details of which have yet to be fully fleshed out – and beefed-up reform of the FA.
Mitt Romney is to gain another significant supporter Thursday when he adds former president George Bush Sr to his burgeoning list of endorsements in the race to become the Republican presidential nominee.
