On her first foreign trip since taking office in the wake of Britain's seismic referendum, May told German Chancellor Angela Merkel that her government would not ask to leave the European Union before the end of 2016 in order to plan a "sensible and orderly departure".
"We will not invoke Article 50 until our objectives are clear, which is why I've said already this will not happen before the end of this year," May said in Berlin, referring to the formal EU mechanism to leave the bloc.
Merkel, who is expected to play a pivotal role in the Brexit talks, said it was in the interests of all that Britain had a "well-defined position" before beginning the negotiations.
"No one wants things to be up in the air -- neither Britain nor the member states of the EU," Merkel said.
"If we look at all matters and challenges facing us, it's most important to have Britain as a partner and we will do so and then negotiate on Britain leaving," she added.
Britain had earlier said it would no longer assume the six-month rotating presidency next July as planned, choosing instead to prioritise negotiations on implementing last month's shock vote to leave the EU.
Estonia's turn, which had been due to start in January 2018, is set to be brought forward by six months to take Britain's place, a spokesman for EU president Donald Tusk said after the announcement.
May has repeatedly asked for patience as her new government maps out its strategy for ending its 43-year-old membership of the EU despite some EU countries wanting Britain out of the bloc as soon as possible.
'Not walking away'
A key sticking point in the Brexit negotiations is likely to be the freedom of EU citizens to live and work throughout the bloc.
Merkel has warned that Britain cannot have continued access to the single market while restricting the freedom of movement - an emotive issue in the June 23 referendum.
May avoided giving details on her position in her first parliamentary question session in London earlier this week - a time-honoured ritual seen as a test of British political leadership.
She also mocked the opposition Labour and Liberal Democrat parties and dodged criticism about past undiplomatic comments made by her choice for foreign minister - top Brexit campaigner Boris Johnson.
May backed Britain's continued membership of the EU.
Several commentators heard echoes of Thatcher in her barbed comments, with the Independent daily commenting that she was "eerily reminiscent" of the late so-called Iron Lady.
Observers in both Britain and Germany have drawn comparisons between Merkel and May: both pastors' daughters with supportive husbands, happy to stay out of the limelight, who rose to become leaders of centre-right parties.
They also share a love of Alpine hiking.
Given the importance of a relationship seen as key to the future negotiations, both leaders were at pains to stress their desire for close ties.
"I've been clear that Brexit means Brexit and the UK is going to make a success of it," May said, but stressed that Britain was "not walking away from our European friends".
"It's in that constructive spirit I've come here today to lay the foundation for a strong relationship in the months and years to come," she said.
Following a working dinner with Merkel, May will travel to Paris for talks with French President Francois Hollande.
May is likely to have tougher ride with the Socialist leader than with Merkel.
Hollande has a presidential election looming next year and is coming under pressure from the far-right National Front, which wants France to leave the EU too.