The phrase "a former contributor" is correct and usable in written English.
It can be used to refer to someone who has previously contributed to a project, publication, or organization but is no longer actively involved.
Example: "The article was written by a former contributor who had extensive experience in the field."
Alternatives: "an ex-contributor" or "a past contributor".
Jack Stack, a former contributor to this blog, popularized the concept with his book "The Great Game of Business".
Briggs also is a former contributor to the humorous Uncle John's Bathroom Reader series, which includes short sections on history, sports, jokes, trivia, and more.
Najam Sethi, the country's most high-profile liberal commentator (and a former contributor to this newspaper), has taken to travelling in an armoured vehicle.
Taylor told the NUJ he is a former contributor to the Daily Express and remains a buyer of the newspaper, and therefore does not "hold grudges".
The first is "Neutrino Hunters" by Ray Jayawardhana, a professor of astrophysics at the University of Toronto (and a former contributor to The Economist).
Karl Ludvigsen, a historian of Mercedes-Benz and a former contributor to Automobile Quarterly, called Mr. Bailey's periodical an indispensable part of any serious car lover's library.
Pelton "has a list of ex-guidebook writers a mile long, and they all hate him with a passion," one former contributor wrote in a letter to The Times.
Mr. Wright, a Pulitzer Prize winner (and former contributor to Texas Monthly) based "Going Clear" on a 2011 article in The New Yorker about the filmmaker Paul Haggis's defection from Scientology — which Mr. Wright said had declined from what he calls its fun early days under its founder, L. Ron Hubbard, to its days of fear under its current leader, David Miscavige.
Hunter S. Thompson, probably the magazine's most famous former contributor, was a stunning stylist but a noted fabulist.
As Thomas de Waal, a well-known commentator (and former contributor to The Economist) notes, Nagorno-Karabakh is hardly a foreign-policy priority for outsiders.
Just this last weekend, tech blog Gizmodo's Twitter account was hijacked by a hacker who had breeched former contributor Mat Honan's iCloud account, allowing the hacker access to Honan's Macbook Air, iPhone, iPad and Twitter account.
