Johnson won a commanding majority in Britain's Parliament, giving him the power to deliver Brexit, though trade talks with the EU are set to drag on for months, if not years.
UK shares exposed to Britain's economy surged, with the benchmark FTSE 100 index gaining more than 2% at one point as a rally in utilities, retailers, housebuilders and banking stocks offset the drag from a jump in sterling.
The pound rose to 19-month high against the U.S. dollar and shares in Europe rose to near all-time highs as investors cheered the likelihood of an orderly Brexit after Johnson's landslide victory.
MSCI's gauge of stocks across the globe gained 0.32%, while the pan-European STOXX 600 index rose 1.25%.
Both MSCI's gauge of global stock performance and the three main U.S. equity indices hit record highs.
But stocks on Wall Street pared initial gains on news of a preliminary accord on a U.S.-Sino deal. Given the contentious nature of the 17-month trade war, investors were slow to fully embrace the news, as both sides have engaged in brinkmanship.
The back and forth between China and the United States is emblematic of a great power struggle, said James Clunie, manager of the Jupiter Absolute Return Fund.
"If there are two great countries locked in a strategic war, which is what a great power struggle is, then that is not going away, that is probably with us for a long time," Clunie said.
The Dow Jones Industrial Average fell 101.47 points, or 0.36%, to 28,030.58. The S&P 500 lost 11.88 points, or 0.37%, to 3,156.69 and the Nasdaq Composite dropped 18.12 points, or 0.21%, to 8,699.20.
Earlier in Asia, Japan's Nikkei climbed 2.5% to a 14-month high and Shanghai blue chips advanced 2%.
Oil rose to its highest in nearly three months as investors cheered progress in resolving the U.S.-China trade dispute and the decisive general election result in Britain.
Brent crude, the global benchmark, rose 47 cents to $64.67 a barrel. U.S. West Texas Intermediate (WTI) was up 41 cents to $59.59.
During the session, both contracts jumped to their highest since Sept. 17, with WTI topping $60 a barrel.
Gold prices were little changed as risk appetite got a boost from progress in the U.S.-China trade talks, though investors remained cautious.
The dollar fell against a basket of currencies as the prospect of a China-U.S. trade deal and the Conservative Party election victory in Britain sapped safe-haven demand for the greenback.
The dollar index fell 0.23%, with the euro down 0.06% to $1.1121.
The Japanese yen strengthened 0.07% versus the greenback at 109.25 per dollar. Sterling last traded at $1.3328, up 1.26%.
U.S. benchmark 10-year Treasury notes rose 23/32 in price to yield 1.8208%,
(Reporting by Herbert Lash) ((email@example.com; 1-646-223-6019; Reuters Messaging: firstname.lastname@example.org))