In 2012, a Taliban gunman shot her in the head for advocating education for girls in her native Pakistan. On Friday, Nobel Peace laureate Malala Yousafzai completed her schooling in Britain, calling the achievement "bittersweet".
"Today is my last day of school and my first day on @Twitter," she wrote on her newly opened account, which gained more than 134,000 followers in three hours.
Yousafzai, who will be turning 20 this month, had been attending a school in the city of Birmingham where she was treated after the shooting in October 2012.
After blogging and campaigning for girls' education in her native Swat valley, she was shot as she rode back to her village on a bus after taking an exam.
Yousafzai has since become a global icon for girls' education, winning the Nobel Peace Prize in 2014.
"Graduating from secondary school (high school) is bittersweet for me," she tweeted, adding: "I know that millions of girls around the world are out of school and may never get the opportunity to complete their education".
But she said she was "excited" about her future and promised to continue "fighting for girls".
Yousafzai has excelled at school and is awaiting the results of her A-level exams next month.She has been offered a place to study at Oxford University.
She has chosen to study Philosophy, Politics and Economics, a prestigious course that has produced many British politicians and world leaders including late Pakistani prime minister Benazir Bhutto.