Kinney's interest in music was developed at an early age. He got his first drum kit when he was 5. By the age of 9, he was keeping the beat for his grandfather's band, The Cross Cats, and traveling the Northwest playing small venues. Kinney grew up in Renton, Washington, where he attended Liberty Senior High School in the Issaquah School District.
Sean Kinney met up with Alice in Chains when he was dating the sister of bassist Mike Starr. Through Starr, he was introduced to Jerry Cantrell who introduced them both to Layne Staley. Since the band's inception, Kinney has been the only drummer. He also sang chorus vocals through a megaphone on the hidden song from Sap entitled "Love Song". The album was named after a dream Kinney had about the band recording some light acoustic songs for an album they name Sap, because it's "sappy." Sean plays a large role in the presentation of the band, having helped design artwork and stage setups for most of the band's albums and tours.
In 1995, Alice in Chains were contemplating making a 3rd studio album, when it was official Kinney drew out artwork for the cover and liner notes. The cover features a three legged dog, reason being, according to band lore, "there was a dog with three legs that always used to chase Sean around when he was doing his paper routes, it creeped him out!" In the music video for Grind, it shows a three legged dog (similar to the one that allegedly used to chase Kinney) walking up a stairway with an elderly man. The dog used in the video belongs to Jerry Cantrell, named Sunshine.