Tries from Thomas Combezou and Benoit Paillaugue, who converted both and also booted three penalties, gave the home side the victory they knew would assure them of a place in the last eight for the first time in their history.
Jonny Wilkinson opened the scoring with an early penalty for Toulon, but Combezou crossed for the game's first try in the eighth minute to put Montpellier in the ascendancy. Paillaugue added the extras and punished Toulon with three penalties in an eight-minute spell midway through the half.
Delon Armitage was yellow-carded for a dangerous tackle six minutes before half-time, and although Toulon withstood Montpellier pressure during his absence, it was not long after his return that the hosts scored again.
Paillaugue darted through to dot down in the 48th minute and with Wilkinson missing two kicks late in the game there was never any danger of a Toulon fightback.
Toulon's first defeat in Pool Six did not prove costly, though, as they finished top and Montpellier took second place, certain to be one of the two best pool runners-up advancing to the quarter-final stage.
The Welsh region had lost their first five matches in Pool Six, but ended their European campaign on a winning note thanks to tries from man of the match Lloyd Williams and replacement Michael Paterson, as well as 16 points from fullback Leigh Halfpenny.
"It was very important to get the victory," said Davies. "That was good today. We got the result and we haven't finished bottom of the table, which is just reward for all the hard work we've put in.''
The Blues trailed for much of the first half and again shortly after the break, having led 9-7 at the interval, but they pulled clear in the end.
With no video referee on duty due to the game not being televised live, Irish referee Peter Fitzgibbon ruled out the score because of a knock-on after consulting his touch judge.
"I thought the referee disallowed a perfectly good try," said Redpath.