Aung San Suu Kyi has become the first non-head of state to address both houses of the British parliament. She was given a standing ovation.
Ms Suu Kyi spent 24 years until 2010 under house arrest during military rule in Myanmar (also known as Burma) and is now allowed to travel overseas.
She earlier met Prime Minister David Cameron at Downing Street.
Ms Suu Kyi appealed for help in restoring democracy to her country and paid tribute to President Thein Sein for his sincerity and commitment to reform in Myanmar.
Commons Speaker John Bercow described her as "the conscience of a country and a heroine for humanity".
In her address in Westminister Hall she said it was important to empower the people and now was her country's time of greatest need.
"I am here in part to ask for practical help, help as a friend and an equal, in support of the reforms which can bring better lives, greater opportunities, to the people of Burma who have been for so long deprived of their rights and their place in the world,'' Ms Suu Kyi said.
"My country today stands at the start of a journey towards, I hope, a better future. So many hills remain to be climbed, chasms to be bridged, obstacles to be breached.
"Our own determination can get us so far. The support of the people of Britain and of peoples around the world can get us so much further."
Ms Suu Kyi concluded her speech by saying there was a lot more work to be done before reform was complete.
"I would ask that our friends, both here in Britain and beyond, participate in and support Burma's efforts towards the establishment of a truly democratic and just society,'' she said.
