The Lions (0-5) had tied the game at 24-24 when Charlie Batch hit Desmond Howard with a 36-yard touchdown pass down the right sideline on a fourth-and-10 play with 1:18 left.
It was the second straight game-winning field goal for Nedney, who kicked a 49-yarder in overtime in last week's 31-28 victory over Tampa Bay.
Tennessee coach Jeff Fisher signed Nedney to a five-year, $6 million contract in the offseason after waiving veteran kicker Al Del Greco, who struggled last season.
Playing for his sixth NFL team in a six-year career, Nedney kicked three field goals in a listless first half, after which the Titans (2-3) trailed, 14-9.
Detroit appeared on its way to padding the lead early in the third quarter, but a 40-yard field goal attempt by Jason Hanson was blocked by Henry Ford and returned 69 yards for a touchdown by Donald Mitchell. McNair hit rookie Drew Bennett on a two-point conversion to give Tennessee a 17-14 advantage.
Detroit tied the game on a 23-yard field goal by Hanson with 9:38 left in the fourth quarter.
But three-time Pro Bowl tight end Frank Wycheck starred on Tennessee's ensuing drive, catching passes of 21 and 29 yards before capping it with a six-yard touchdownthat gave Tennessee a 24-17 lead with 4:41 remaining.
Wycheck finished with seven receptions for a career-best 100 yards. The Titans have won nine straight against NFC teams.
With Washington's overtime win over Carolina, Detroit became the lone winless team in the NFL. The Lions are 0-5 for the first time since losing their first five games in 1989.