The major studios, who in many cases tacitly went along with the McCarthyite witch-hunts, will be asked to restore the names of ten writers on the films, made between 1952 and 1971, from Born Free to Inherit the Wind. One of the few surviving writers, Bernard Gordon, 78, thanked the Guild for "correcting the record and giving credit where it is long overdue".
But he also said the action came four decades too late to help his Hollywood career. Among the films Mr Gordon wrote was Hellcats of the Navy, a 1957 comedy which was the only film in which Ronald Reagan and his future wife Nancy Davis appeared together. Mr Gordon's name will now be added to that of a second writer on the film, David Lang.
"I am sure angry at the way I was treated by all the major studios," Mr Gordon told the New York Times. "They blacklisted me, and I couldn't get any work in this damn town."
He later built a successful career in Europe. A prolific writer, he will get new credits on seven films. The Guild, with 7,500 members on the west coast, acts as the official arbiter of writing credits.
They may go unnoticed by audiences, but are the lifeblood of scriptwriters, who often complain of being at the bottom of the Hollywood food chain, their work butchered by producers and petulant actors.
A credit meant a guarantee of more work, and a rise in salary, particularly in the 1950s and 1960s, when writers were more firmly under the studios' thumb than they are today. Pay rates would be directly linked to the number of credits a screenwriter had under his belt.
The guild's executive director, Brian Walton, said it was moving to correct these "sad an unfortunate actions of the past".
The films run from The Adventures of Robinson Crusoe, in 1952, to Custer of the West, Earth vs the Flying Saucers, and The Robe. The news came much too late, however, for writer Lester Cole.
In 1966, he adapted Joy Adamson's book of her life with African lions for the film Born Free, but under the pseudonym Gerald LC Copley. While the film was hardly an artistic gem, its irresistible animal footage made it a huge commercial success.
Mr Cole, one of the celebrated "Hollywood Ten", died in 1985, aged 81.
Writer or co-writer on 40 screenplays, he was a founder of the Writers Guild, but also a lifelong socialist who joined the Communist Party in 1934. Before the Second World War he worked on 24 films.
But when he refused to name names before the House Un-American Activities Committee in 1947, he was fined and eventually imprisoned, with his career destroyed.
Unbowed, he ended his 1982 autobiography, Hollywood Red, with a quotation from Friedrich Engels: "Until there is world socialism, man remains in a stage of his prehistory."