The picture was posted on Leno's official Facebook page ahead of Thursday evening's (October 25) broadcast, along with the caption "This is happening tonight… and it's magical. Oh yes, it is magical."
Brand and Lynch shared a peck on the lips as she arrived on set, and the Rock of Ages actor joked: "That kiss on the mouth has taken our relationship to the next level."
"You have really nice teeth for a British person," Lynch told Brand, who responded: "You've got nice lips for a Yank."
Glee star Lynch appeared on The Tonight Show to talk about new animated movie Wreck-It Ralph, while Brand was promoting his new FX comedy show Brand X.
Brand also told an anecdote about his appearance at the London 2012 Olympics closing ceremony, claiming that he had a 'wardrobe malfunction' moments before taking to the stage.
"Well, I enjoyed the bit where it was all the running, the jumping, the skipping, the skylarking, the hullabaloo, the competitiveness, the beads of sweat, that was all lovely," the comedian said of the Olympics in a preview clip for his Tonight Show appearance.
"But when it came to that bit that I had to do... just before I went on stage in that clip... I thought - once they said 'Do you wanna be in the Olympics?' - on some level, I thought, 'I'm an athlete now'.
"So, before I did [my song], I did some limbering up, exercises, but because I don't know how to limber up properly, 'cause I'm not really an athlete, I did it badly... one minute before I had to go on top of that bus... I heard this [ripping] noise, like that, and my trousers tore - a significant distance - and at that point, someone said, 'Right! Get on top of the bus!'"
Brand added that he was offered Scotch tape to fix his trousers, observing: "If Scotch tape bends or folds, it creates these horrible, sharp jagged edges. It was like a prison weapon!"