The mural shows the likely US Republican presidential nominee and the former mayor of London — both populists intent on shaking up their countries’ political establishments — locking lips.
Trump is cradling Johnson’s shock of blond hair in his hand.
The mural in Bristol, southwest England, was commissioned by We Are Europe, a campaign group which wants Britain to remain in the European Union at the June 23 vote.
Johnson is a leading figure in the “Leave” campaign who has been tipped as a possible future prime minister if Prime Minister David Cameron, who wants to remain in the EU, loses the vote.
Meanwhile, Trump has said Britain would be better off outside the EU.
“People need to look at this image and think: ‘Is this the future I want?’” said Harriet Kingaby, one of the founders of We Are Europe.
The 4.5 metre high artwork has echoes of a mural of Soviet and East German leaders Leonid Brezhnev and Erich Honecker known as The Kiss which was painted on to the Berlin Wall in 1990.
Bristol is known as the spiritual home of graffiti artist Banksy, although the Trump and Johnson mural was created by artists Felix Braun and Jack Dones.