Jim worked as the banjo player for Ricky Skaggs and Kentucky Thunder for 14 years until the summer of 2010, when he left the band to focus on his business buying, selling and trading rare pre-war banjos. In the 1980s, prior to his stint with Skaggs, Jim performed for 5 years with Doyle Lawson & Quicksilver. He has 3 solo albums and has performed on many others. He has won the IBMA banjo player of the award 6 times (1999, 2000, 2001, 2003, 2005, 2006), more than any other player, and also won IBMA Instrumental Album of the Year for his Bound to Ride album. Jim has won 6 Grammy Awards.
Jim owns several pre-war Gibson Mastertone banjos, including the famous "Mack Crow" banjo (named after its original owner, it is the only factory-produced gold-plated RB-75 that Gibson ever made.) and the RB-4 previously owned by the late Snuffy Jenkins. Huber Banjos produces a Jim Mills signature model based on the Mack Crow. Jim released a book on pre-war Gibson banjos in 2009, Gibson Mastertone: Flathead 5-String Banjos of the 1930′s and 1940′s.