The Nobel Peace Prize laureate, 20, tweeted on Monday: "5 years ago, I was shot in an attempt to stop me from speaking out for girls' education. Today, I attend my first lectures at Oxford."
Malala was shot in the head on a school bus in Swat Valley in north-west Pakistan on October 9, 2012. She was flown to the UK for treatment, and after her recovery finished her studies at a school in Birmingham.
Thousands of well-wishers responded with messages of congratulations after she posted the picture, and the post was liked more than 150,000 times within hours.
Her brother, Khushal Yousafzai, tweeted in reply: "Sorry for being a headache for the last 5years. So grateful you are still with us. Ik (I know) you miss me but i am coming to oxford in 2years."
She has updated her supporters on her university journey on Twitter previously, using the site to announce that she had got the grades she needed to take up her place at Oxford to study Philosophy, Politics and Economics (PPE), and asking for advice on what to pack.
She did not reveal her grades but earlier this year she told a conference she had received an offer, which was conditional on achieving three As at A-level.
Her career as an activist began in early 2009, when she started writing a blog for the BBC about her life under Taliban occupation and promoting education for girls in Pakistan's Swat Valley.
But her campaign angered local militants and she was shot during an assassination attempt while taking the bus to school.
She was treated at Birmingham's Queen Elizabeth Hospital and, fearing reprisals in her native country, made the city her home.
In 2014 she became the youngest person to be awarded the Nobel Peace Prize and her campaign for children's rights to education across the world has seen her addressing the United Nations on the issue.