Perry pecked the One Direction star when she presented the band with the 'Best Pop Video' award, one of three honours they took home.
Horan later uploaded a photograph of the kiss to his Twitter page, adding the caption: "looks like its official ... me and you."
Perry retweeted the picture, joking: "I'll be your Mrs. Robinson", prompting Horan to reply: "and here's to u mrs.robinson, I guess I can deal with that."
Perry, who was also pictured kissing other members of the band, had previously expressed outrage at an incorrect rumour that One Direction were not performing at the ceremony.
"IF ONE DIRECTION DOESN'T PERFORM ON THE VMA'S I AM GONNA JUMP OFF THIS LEDGE," she wrote, later adding: "oh... it was just a rumour... *steps down*."
Horan and his bandmate Zayn Malik later went to Justin Bieber's house to celebrate their success at the VMAs.