He takes over from Theresa May, whose failure to get her Brexit deal over the line led to her demise.
Johnson has a real job on his hands as the EU looks stubborn and is likely to not renegotiate the withdrawal agreement that May had put together.
Sticking to his game plan to force through a no-deal Brexit, however, will most likely stir up the financial services sector.
The Brexit conundrum
Following confirmation on Tuesday, the financial services sector has reacted to Johnson becoming leader of the Conservative Party.
Leigh Himsworth, portfolio manager at Fidelity International, said: “With Boris Johnson as prime minister, the options facing the UK remain broadly the same: a withdrawal agreement similar to that presented by Theresa May; a general election to win a greater majority for the Conservative party or a new referendum.
“The outcome will depend on how confident Boris feels in his own political power. His support of the Leave campaign gives him leverage over the right wing, while the bluster may win Labour Leave voters. His personal background may help him retain the Tory heartland.
“But the key question is whether he will be able to extend his charm over the Channel.”
Tristan Hanson, multi-asset fund manager at M&G Investments, added: “Attention will immediately turn to Brexit and the 31 October deadline.
“The new prime minister will see if he can negotiate changes to Theresa May’s deal and, if so, will try to get a revised deal through parliament by that date. If not, both he and parliament will be stuck with the same immediate choices as under Theresa May’s leadership.
“The risk of a no deal exit may have risen, but the evidence is that parliament will attempt to thwart such an outcome. The likelihood of a general election has also increased.
“So, the path ahead remains as uncertain and unpredictable as the journey so far.
“Ultimately, whatever the interim steps, the options remain the same whoever is prime minister and whichever party is in government: leave with or without a deal, or remain.”
Not all doom and gloom
There are some in the industry who believe Johnson’s no deal Brexit stance isn’t actually a wild idea.
Jeremy Leach, chief executive at asset management firm Managing Partners Group, said: “The appointment of a new UK prime minister means we are halfway through the period of uncertainty surrounding Brexit.
“Financial markets hate uncertainty, so they will like Boris Johnson’s mantra that one way or another, the UK will be out of the European Union by the end of the year.
“As such, we would expect a bounce in UK and European equities as well as sterling.
“Whether Boris Johnson’s intentions are indeed to leave without a deal, he is right to keep the EU guessing on how committed the UK is to walking away without one.
“The EU played its cards right by giving every indication it was willing to accept a no-deal Brexit when the reality is that Brexit will be a massive upheaval for them too.
“It is in all parties’ interests that trade continues and I have no doubt that the borders will remain open for that.”
Implications for the financial markets
Outside of the deal, what will the newly appointed prime minister mean for the market?
Fidelity International’s Himsworth added: “As far as financial markets are concerned, our eyes remain firmly fixed on sterling, which is reacting, almost by the minute, to the deal/no-deal narrative.
“And while it is easy to argue that the UK equity markets offer great value versus their peer group, this is especially true of a deal or new referendum scenario.
“The jury remains firmly out regarding a no-deal as this would be too much of a step into the unknown.
“We may well look back in a few years’ time and regard this period as quite simply one of the best opportunities that we have seen to invest in UK equity markets.”
Paul O’Connor, head of multi-asset team at Janus Henderson Investors, said: “Growth remains a key concern, with 2019 looking set to be the fourth consecutive year of sub-2% UK GDP growth.
“Confidence is deteriorating across the construction, manufacturing and services sector and among consumers as well. With the economy looking like it is one stumble away from recession, a policy response is needed.
“A 2019 interest rate cut seems increasingly likely and a Johnson fiscal stimulus a near certainty. While both of these can help cushion the impact of Brexit-related uncertainty on the economy, a full restoration of confidence seems unlikely until the big issue gets resolved.”
Outside of Brexit
Others, however, were keen to point Johnson in the direction of priorities other than the UK’s departure from the European Union.
Helen Morrissey, pension specialist at Royal London, said: “While Boris’s in-tray is likely to be straining under the weight of Brexit related issues there’s a domestic agenda that has been in limbo for far too long.
“We call upon the prime minister to devote some time to pressing issues such social care funding and the pensions bill which will allow the industry to make much needed progress with initiatives, such as the pensions dashboard.”