The coming few weeks demand some big decisions from Mr Johnson and his cabinet.

So what are they - and what does the BBC's assistant political editor Norman Smith think are the key factors at play?

One of Mr Johnson's headline pledges in his election campaign was to increase connectivity for all, so the creation of a UK-wide 5G mobile network could play a major part in keeping that promise.

Chinese firm Huawei is a leader in the field and wants to supply the kit for the network.

But while the technology is recognised, there are fears about allowing a company with strong links to the Chinese government into such crucial infrastructure.

The US in particular has voiced its concerns, saying it "would be madness" to use the firm's technology and warning the decision would lead to a review of intelligence-sharing with the UK.

But Huawei has denied posing any threat to security and suggested the worries were about frustrating its progress in the sector, rather than anything more sinister.

A decision was due last year, but it was delayed, prompting anger from UK mobile companies who are keen to crack on.

The government is expected to make its final call on Tuesday, but Mr Johnson hinted with a day to go that there would be some use of the tech firm's equipment.

He told reporters: "We are going to come up with a solution... to have access to fantastic technology, fantastic communications, but also [to] protect our security interests and protect our key partnerships with other security powers around the world."

HS2 or not to HS2

Another pledge from the PM was to improve physical infrastructure in the UK - namely transport - and Mr Johnson is now smack bang in the middle of the arguments over one of the biggest projects, High Speed Rail 2 (HS2).

The blueprint sees a first line being built between London and Birmingham - to carry bigger trains and allow for more passengers - before a second "v-shaped" phase, taking services from Birmingham to Manchester and Leeds.

But concerns have been raised over the cost - which is expected to pass £100bn - and whether the need for stronger rail links from east to west in the north of England should take precedence.

The government commissioned a review of HS2 after Mr Johnson was handed the keys to No 10 last summer, with Transport Secretary Grant Shapps saying it was "responsible" to see whether the benefits really "stack up".

But the pressure is mounting for a decision, especially after repeated leaks from the review.

A final call on whether to continue with the project is expected in February.

Northern Rail ruling

It isn't just brand new infrastructure under the looking glass - Mr Johnson and Mr Shapps have also promised to address the ongoing troubles with Northern Rail.

The firm in charge, Arriva Rail North, has come under heavy criticism for its performance, and politicians - including Labour's Makerfield MP Yvonne Fovargue - and residents served by the line have called for the franchise to be removed.

Mr Johnson said the government was "developing contingency plans" for a replacement, while Mr Shapps said stripping the firm of its franchise was an option.

But the transport secretary said he was also evaluating a proposal from the train operator on options for continuing.

A final call on the controversial issue will have to be made soon.

Time for a reshuffle

After Mr Johnson won his majority, the word from Westminster sources was to expect a big reshuffle of his cabinet come February.

His initial appointments when he took over in July 2019 seemed to be focused around rewarding Brexit backers and his own supporters from the Tory leadership contest.

But now he has five years in power, commentators believe his choices will show what direction he wants to take as prime minister.

So, who will be out and who will be in?

The only person we know for certain who will be out of a job - or his current one, at least - come 1 February is Brexit Secretary Steve Barclay, but that is because his department is being shut down.

The rest, for now, is speculation. But it is another big and defining decision for the PM to take.

The EU negotiations begin

Last but not least, Brexit... Mr Johnson based his whole election campaign on "getting Brexit done", but once the UK leaves the EU on 31 January, there is the small matter of negotiating a trade deal with the bloc to contend with.

The PM has said he's ready to get talks started the very next day, but he has also put a hard deadline on negotiations - the end of the year.

Mr Johnson has insisted he can get a deal done in 11 months. However, other parties involved, including the EU's negotiator Michel Barnier and Irish PM Leo Varadkar, have cast doubt on that timeline.

It's not just a question of timings, either. Mr Johnson also needs to decide on his game plan - what does he actually want to get out of an agreement with the EU?

There have been slightly mixed messages from the Treasury on just how close the UK wants to stay aligned with Brussels, but we should find out the real intentions in the coming days.