Changes are in effect across all Australian states as of Sunday, Lifeblood said in a statement on its website.
"Following the approval of our submissions by the TGA, subsequent agreement by all Australian governments, and an update of Lifeblood systems including the donor questionnaire form, we are pleased to report this change was applied on 31 January 2021 and is now in place for all applicable sexual-activity-based blood donation deferral policies," the statement said.
"At Lifeblood we're continuing our focus to make it easier for all Australians to give blood, while always ensuring Australia's blood and blood products are as safe as possible for blood recipients."
Gay men had previously been banned from donating during the height of the Aids epidemic in the 1980s, with those rules lingering for decades.
The new change came following a push for blood donors during the Covid-19 pandemic, with MPs Alex Greenwich and Dr Time Read vocally supporting the move in their respective states of NSW and Victoria.
However, the decision not to scrap the celibacy period altogether has attracted criticism from LGBTI advocacy groups including just.equal.
Their spokesman and long-time blood equality advocate, Rodney Croome, said blood-donors should be screened based on individual factors and not gender or sexual orientation.
Croome said a recent study published in the American Journal of Public Health found individual measures "are equally effective in protecting the blood supply".
"This landmark study confirms that reducing the celibacy period is tinkering at the edges.
"To remove discrimination and increase the supply of safe blood, Australia must adopt a new approach to blood donation that screens donors for their individual sexual risk rather than the gender of their sexual partner.
"The current governments of both the United States and the United Kingdom are committed to replacing their gay blood bans with individual risk assessment, and it's time for Australia to do the same.
"We call on the Australian Red Cross Lifeblood Service to ditch a policy American experts label 'illogical and unsubstantiated', and adopt a policy based on scientific evidence instead."
Croome said the study also showed that among gay men who would donate blood, the prevalence of HIV is lower than in the general population.