Alan Turing, the celebrated mathematician and wartime codebreaker, has been granted a royal pardon 59 years after his death.

Often described as the "father of computer science", Turing – who studied as an undergraduate at King’s College and became a fellow there at the age of 22 – has been granted a pardon under the Royal Prerogative of Mercy following a request made by the government’s justice secretary, Chris Grayling.

Turing worked as a cryptanalyst at Bletchley Park during the Second World War, where he developed the machine that deciphered the Enigma codes used by German U-boats. Historians argue that his work significantly aided allied efforts; some say it shortened the war by two years.

In 1952, at a time when homosexuality was still illegal, he was convicted of gross indecency for his relationship with a 19-year-old man. Turing chose to undergo chemical castration by female hormone replacement rather than serve a prison sentence.

When he died two years later in June 1954 an inquest found that he had died from cyanide poising and concluded that Turing had committed suicide. This finding is contested.

Announcing the pardon, Grayling said: “Dr Alan Turing was an exceptional man with a brilliant mind. His brilliance was put into practice at Bletchley Park during the second world war, where he was pivotal to breaking the Enigma code, helping to end the war and save thousands of lives.

“His later life was overshadowed by his conviction for homosexual activity, a sentence we would now consider unjust and discriminatory and which has now been repealed.

“Dr Turing deserves to be remembered and recognised for his fantastic contribution to the war effort and his legacy to science. A pardon from the Queen is a fitting tribute to an exceptional man.”

The granting of a royal pardon is rare.  It is usually extended only when the convicted person has been found innocent of an offence and a family member has made an official request.

The pardon states: “Now know ye that we, in consideration of circumstances humbly represented to us, are graciously pleased to grant our grace and mercy unto the said Alan Mathison Turing and grant him our free pardon posthumously in respect of the said convictions.”

The pardon is the culmination of a long campaign to clear Turing’s name.  In 2009 prime minister Gordon Brown issued an “unequivocal apology” for Turing’s treatment.  Last year an e-petition requesting a pardon gathered 37,404 signatures before being shut down.

Speaking to Varsity, Cambridge MP Julian Huppert, who has been involved in the campaign to obtain a pardon and brought the matter to the House of Lords in 2012, said: “Alan Turing was a great man, who saved this country. However, we treated him abysmally in response. This has been a stain on this Nation's character for decades, and I am delighted it will finally be expunged.

“Society would no longer tolerate the idea of chemical castration for people who are homosexual, and it is right that we have now allowed anyone alive to have convictions deleted for consensual homosexual behaviour. But around the world, people are still treated too badly just for being homosexual.”

Charlie Bell, CUSU's LGBT officer, said: “It's great news to see an unbelievably barbaric set of accusations quashed by this Royal Pardon, which is the culmination of a lot of work to clear the name of Dr Turing, one of Cambridge's, and indeed one of the UK's, greats.

“However, whilst a posthumous pardon will bring comfort to many who knew and loved Alan Turing, the UK government, and all of us, should be taking a stand against the disgraceful and disgusting way LGBT people are still treated around the world.”

Read "The pardon of Alan Turing: too little, too late", here