But what are the key issues that will be waiting in Boris' in-tray as the former London Mayor takes up his new role?
The European Union
Much of the hard work over negotiating an exit from the bloc has been hollowed out of the Foreign Secretary brief with the creation of a Brexit Secretary.
But Mr Johnson remains the man who will represent the UK at meetings with foreign ministers in Brussels - a place he made his journalistic name through a relentless string of excoriating dispatches.
He will return to the City on Sunday for an informal meeting over dinner with counterparts to discuss the Brexit vote.
The following day, he will attend his first EU Foreign Affairs Council.
Britain is set to take over the rotating six-month presidency of the EU Council next year, but it is widely expected that the Government may opt out of the role.
Dealing with the dual terror of the civil war sparked by Bashar Assad's brutal dictatorship and the rise of Islamic State will be the most pressing international issue facing the Foreign Secretary.
Johnson suggested Britain should do a deal with the devil and work with Vladimir Putin and Assad to rid Syria of IS in his Daily Telegraph column in December 2015.
He backed a "joint enterprise" between Russia and the Syrian regime but said: "It does not mean I trust Putin, and it does not mean that I want to keep Assad in power indefinitely".
The comments were in stark contrast to government policy and Johnson's position on Syria now he is in office will be keenly awaited.
US Secretary of State John Kerry will discuss strategy with European counterparts at a breakfast in Brussels on Monday.
Relations with Moscow have been restored to their traditional icy low in the face of an increasingly aggressive Putin presidency.
One of David Cameron's last acts as prime minister was to urge Brussels and Nato to stand firm in face of any fresh aggression by Russia amid fears Britain's withdrawal from the EU will weaken its resolve to stand up to Putin.
Britain is sending 650 British troops to eastern Europe as part of a Nato deployment.
EU sanctions against Russia following the annexation of Crimea will come up for renewal in early 2017.
Mr Johnson will host meetings with international counterparts, including Mr Kerry, in London on Tuesday.
The country has been riven by civil war, with Saudi-led forces supporting the Yemeni government pushed into exile by Houthi rebels.
Attempted ceasefires have failed to stop the killing.