The New Zealander, whose penalty secured World Cup final glory for the All Blacks against France in Auckland last month, marked his home debut in style.
Donald created Bath's opening try and then almost scored the second following a lengthy interception sprint, while he also slotted two penalties to get his team up and running in Heineken Cup Pool Three.
After losing away to Glasgow last weekend, Bath knew they could not afford a second successive defeat and effectively risk pool stage elimination, a fate seemingly destined for their fellow English representatives Northampton, Gloucester and London Irish.
But although they took charge early on, with wing Olly Woodburn and prop David Flatman scoring tries, Montpellier hit back through the efforts of wing Martin Bustos Moyano.
He scored a try and added eight points from the boot, hauling Montpellier back into contention after they trailed by 13 points early in the second-half.
It was a fine recovery by the tournament debutants, who could easily have folded during Bath's period of dominance, and they might yet have a say in a pool currently led by Leinster.
Donald's first start apart, former England captain Lewis Moody also featured in a Bath side that knew any further Heineken slip-ups would leave their quarter-final hopes hanging by a thread.
Montpellier, meanwhile, who were beaten narrowly by Toulouse in last season's French championship final, looked to build on a draw against Heineken Cup holders Leinster eight days ago.
Bath made a blistering start, establishing an 8-0 lead after just nine minutes as Montpellier struggled to cope with the fluency of their attacking game.
Donald was at the heart of Bath's onslaught, kicking a short-range penalty and then floating a pinpoint long pass to an unmarked Woodburn, who finished off in the corner.
Donald's conversion attempt hit the left-hand post, but Bath were up and running before striking with another try that left Montpellier floundering.
The visitors looked to be stringing together a threatening attack, yet Donald intercepted a midfield pass and sprinted 80 metres into Montpellier's 22 before he was caught by their cover defence.
Donald managed to free centre Dan Hipkiss, and after he was hauled down just short of the line, Bath worked Flatman over on an overlap for a 13-point advantage.
And to make matters worse for Montpellier, they were temporarily reduced to 14 men when their star fly-half Francois Trinh-Duc was sin-binned by referee Alain Rolland for killing Bath ball.
With Trinh-Duc still off, Bustos Moyano kicked a penalty from halfway to cut Bath's advantage, but he could not find the target just two minutes later from closer range.
Bath had gone into their shells after such a livewire opening, and Bustos Moyano missed another penalty on the stroke of half-time as the home side retained a comfortable lead.
Donald took a hefty blow early in the second period, but he dusted himself down to boot a 44th-minute penalty before Montpellier finally stirred into action.
Even if there was a huge slice of luck about Bustos Moyano's try - the scoring pass from lock Thibaut Privat was clearly forward - they were back in contention at 16-13 adrift after Bustos Moyano landed a touchline conversion and then an angled penalty.
Montpellier had scored 10 points in five minutes, and with Bath losing their early attacking verve, the game appeared set for a tense final quarter.
It became a highly-attritional contest as darkness descended on the Recreation Ground, although Bath had at least kept Montpellier pinned deep inside their own half.
Olly Barkley, sidelined since March because of a broken leg, made his comeback off the bench five minutes from time, and he had an immediate opportunity to calm Bath's nerves with a long-range penalty kick, but it dropped just short.
Bath, though, possessed sufficient composure to successfully wind down the clock and collect a crucial four points.
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