Mayer has a number of tattoos. These include: "Home" and "Life" (from the song title) on the back of his left and right arms respectively, "77" (his year of birth) on the left side of his chest, and a koi-like fish on his right shoulder. His entire left arm is covered in a sleeve tattoo that he acquired gradually, ending in April 2008; it includes: "SRV" (for his idol Stevie Ray Vaughan) on his shoulder, a decorated rectangle on his biceps, a dragon-like figure on his inner arm, and various other floral designs. In 2003, he got a tattoo of three squares on his right forearm, which, he has explained, he will fill in gradually. As of 2008, two are filled.

He is an avid collector of watches and owns timepieces worth tens of thousands of dollars. Mayer also has an extensive collection of sneakers, estimated (in 2006) at more than 200 pairs.

Mayer dated Jennifer Love Hewitt briefly in 2002. In a comedy routine in May 2006, he joked that they never consummated their relation