Albert Barnes Commentary 2 Samuel 6:10

"So David would not remove the ark of Jehovah unto him into the city of David; but David carried it aside into the house of Obed-edom the Gittite." — 2 Samuel 6:10 (ASV)

Obed-edom was a Levite from the family of Merari and a son of Jeduthun, who was also a Merarite (1 Chronicles 15:18–24; 1 Chronicles 16:38). He was a porter, a harp player, and one of the Levites specially designated to take part in the musical services when the ark was brought to Zion and to minister before it after it arrived.

He is called a Gittite, perhaps because he was from Gath-Rimmon in Manasseh, a city that belonged to the Kohathites (Joshua 21:25). A marriage to a Kohathite, or some other reason, would account for him living in a Kohathite city.