The UK-focused FTSE mid-cap index jumped 5pc to a record high, pushing the broader pan-European STOXX 600 up 1.6pc and putting it on course for its best day in two months.
The blue-chip FTSE 100 also advanced 1.7pc, as solid gains in banks and utilities helped the export-heavy index shrug off the impact of a surge in sterling, which typically weakens sentiment towards component companies.
Dublin's ISEQ, also considered a barometer of Brexit sentiment, jumped to a 12-year high.
Markets believe a Conservative Party win would enable Johnson to deliver Brexit within weeks, easing fears that the United Kingdom could crash out and ending 3-1/2 years of uncertainty over the shape of the country's exit from the trading bloc.
"The big issue has been the lack of direction and that goes away, which is why sterling is rallying and Gilt yields are back up and domestically-focused equities are gaining," said Gaurav Saroliya, director of global macro strategy at Oxford Economics.
The benchmark European index is now just two points shy of a record high hit in 2015.
It is also on track to end the year almost 20pc higher, its biggest annual gain in a decade, as investors turn optimistic about another major economic issue - the prolonged U.S.-China trade war.
Trade-sensitive German shares jumped 1.3pc on Friday after a report the United States would suspend tariffs on Chinese goods set to kick in on Sunday and cut others in return for Beijing buying more American farm goods.
All major country indexes were trading higher.
The European travel and leisure index added 4.1pc, boosted by a 7.5pc to 9pc surge for Brexit-sensitive airline stocks such as easyJet, International Consolidated Airlines Group, and Ryanair Holdings plc.
In corporate news, Delivery Hero gained more than 15pc as it agreed to buy South Korea's top food delivery app operator Woowa Brothers for $4 billion and form a joint venture. Its shares helped the retail sector rise 3.3pc.
German consumer goods company Henkel slipped 3.2pc as the consumer goods company said it expects its EBIT margin to fall to 15pc in 2020.