The 27-year-old from Lancashire left the notorious Keng Tung prison where he had been sentenced to 17 years for speaking out against the military junta.
Mr Mawdsley, accompanied by his mother Diana, was expected to arrive at Heathrow early today. He gave a press conference in Bangkok in which he betrayed no signs of his ordeal.
Last night Mr Mawdsley's father, a London property manager, said he would not celebrate until his son was beyond the Burmese government's reach. "I've lost a lot of sleep over James in the past year - another night won't make much difference," he said.
Rachel Goldwyn, 29, the British student who spent two months in a Burmese jail last year for singing protest songs, also gave a guarded welcome to news of Mr Mawdsley's release.
" I'm still not cracking open the champagne, but we are getting closer to the stage where we can celebrate."
Mark Rowland, of the Jubilee Campaign, a group which has worked for Mr Mawdsley's freedom, said: "This is an epic example of one individual's sacrifice to challenge oppression. The international community must listen and take action to stop this systematic abuse of human rights."
The former Bristol University student was jailed within hours after being arrested for carrying pro-democracy leaflets in August.
Earlier this month, the United Nations ruled he was being held unlawfully.
Mr Mawdsley was beaten by guards at Keng Tung on three successive days last month, His nose was broken, and his food was contaminated after he wrote protest slogans on cell walls.
After announcing Mr Mawdsley's release, Robin Cook, the foreign secretary, said: "I acknowledge the tireless efforts of his family, friends and others these efforts, coupled with diplomatic pressure we applied through our embassy in Rangoon and internationally, played a part in ensuring James is a free man today."
