Theresa May has delivered a farewell speech in Downing Street before tendering her resignation to the Queen.
She wished new Prime Minister Boris Johnson and his government well, adding: “Their successes will be our country’s successes.”
Earlier, Mrs May faced MPs’ questions for the final time and looked visibly emotional as she left to applause.
Mr Johnson will speak outside No 10 too, before announcing several senior cabinet appointments.
He is expected to use the opportunity to increase the number of women in full cabinet positions and boost the representation of ethnic minorities.
During his journey to Buckingham Palace to accept the Queen’s invitation to form a government, Mr Johnson’s car was briefly held up by protesters from Greenpeace, who formed a human chain across The Mall.
Mrs May gave her final speech in Downing Street before heading to Buckingham Palace.
She said serving as prime minister had been “the greatest honour” and thanked all those who had worked with her.
“This is a country of aspiration and opportunity, and I hope that every young girl who has seen a woman prime minister now knows there are no limits to what she can achieve.”
Mr May was briefly interrupted by a protester shouting “Stop Brexit!” but responded by saying: “I think the answer to that is – I think not.”
A short time earlier, at her final PMQs, Mrs May said she would continue as a constituency MP and was “looking forward to asking the questions” in future.
She said she was happy to hand over to a successor committed to delivering Brexit and creating “a bright future for this country”.
A number of MPs took the opportunity to praise her commitment to office and her achievements on issues like modern slavery, mental health and getting more women into politics.
Labour leader Jeremy Corbyn acknowledged Mrs May’s “respect for public service”, but criticised her record on the economy, homelessness and Brexit.
He asked whether she would consider joining him “in opposing the reckless plans of her successor”.
She, in reply, listed what she felt were her successes, including school improvements, more employment and greater home ownership.
“At its heart, politics isn’t about exchanges across these despatch boxes, nor about eloquent speeches or media headlines,” she said. “It is about the difference we make every day to the lives of people up and down this country.”
In a parting shot at Mr Corbyn, she added: “As a party leader who has accepted when her time was up, perhaps the time is now for him to do the same.”
Former London mayor Mr Johnson won a decisive victory over Foreign Secretary Jeremy Hunt in a ballot of Tory members – gaining a 66.4% total share of the vote.
Conversations are said to be “ongoing” between Mr Hunt and Mr Johnson about the foreign secretary’s next role.