The decision by the Criminal Cases Review Commission - the first by the independent miscarriage of justice watchdog since it began work in April this year - comes a week ahead of a televised admission, on Channel 4's Trial and Error programme, by self-confessed IRA bomb-maker Dessie Ellis that electronic circuit boards linked to McNamee bore a close resemblance to those Ellis had been convicted of constructing.
McNamee, sentenced to 25 years for conspiracy to cause the 1982 explosion, was described by the prosecution at his 1987 trial as the IRA's "master bomb maker."
But the commission said yesterday that the conviction should be reconsidered following inquiries into scientific and fingerprint evidence and non-disclosure of evidence at the time of McNamee's first appeal in 1991.
McNamee, 37, a former electronics engineer from Crossmaglen, Co Armagh, has persistently denied membership of the IRA and protested his innocence.
His conviction turned on the discovery of his fingerprints on tape found in two IRA arms dumps, and on a battery which survived the explosion.
McNamee said in his defence that rolls of that kind of tape could have been handled by numbers of people in the electronics factory where he worked, while he had repaired thousands of CB radios which contained similar batteries.
The trial heard that there were more than 100 prints on the contents of the arms caches, which the prosecution accepted were from innocent parties.