May hit the ground running and had announced some of her key frontline Cabinet posts within minutes of walking into her new Downing Street office.
In her first move, she replaced UK Chancellor George Osborne with close friend Hammond, whose role as foreign secretary in David Cameron's Cabinet will be taken over by Johnson.
"The Queen has been pleased to approve the appointment of Rt Hon Philip Hammond MP as Chancellor of the Exchequer. The Rt Hon George Osborne MP has resigned from government," a Downing Street statement said on Wednesday evening.
While Osborne's exit came as less of a surprise, being a close Cameron aide, Johnson's appointment as foreign secretary was more unexpected. He had led the charge for the Brexit camp in last month's European Union referendum and had been widely expected to step into Cameron's shoes as Prime Minister.
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He had also come out strongly in support of Andrea Leadsom, May's last remaining opponent to the post of Conservative party leader before she withdrew on Monday.
As was expected, May also created a new portfolio of so-called "Brexit secretary" and appointed David Davis, a former shadow home minister, to head the new department in charge of Brexit.
Another new department is that of international trade, indicating the importance of striking new trade agreements in the wake of Brexit, and the man in charge will be Liam Fox - who had also been among the contenders for the post of Conservative party leadership.