The lifetime ban on blood donations by homosexual and bisexual men will be lifted in England, Scotland and Wales.
Ministers have agreed to let men who have not had sex with another man in the past 12 months to donate from November.
The restrictions were put in place in the 1980s to prevent the risk of HIV contamination.
However, the latest medical evidence presented to a government panel argued the ban could no longer be justified.
Ministers in the three countries accepted the argument and said they would be relaxing the rules. Northern Ireland is expected to make a decision soon.
The National Blood Service screens all donations for HIV and other infections. However, there is a "window period" after infection during which it is impossible to detect the virus.
In the UK, a lifetime ban was introduced in the early 1980s as a response to the Aids epidemic and the lack of adequate HIV tests.
