Rhodri Jones’ converted try just after half time proved decisive with both sides having tries chalked off in the second half.
Newport had taken an 11th minute lead through a Josh Reynolds try, but the Drovers responded seven minutes later through Adam Warren.
It completes a league and cup double for Llandovery, who also topped the Premiership table at the end of the regular season.
Newport were left to rue missed opportunities and a number of unforced errors that ultimately cost them.
They came into the game on a run of 15 consecutive victories since they had last tasted defeat – which was also at Church Bank back in November. They knew a 16th would secure them a first league title since 2004.
After an explosive start, it was Newport who drew first blood with loosehead prop Josh Reynolds finishing off a classic forwards try after some patient build-up play. Matt O’Brien – on his 200th Newport appearance – added the extras.
Josh Reynolds powers over to score the opening try for Newport
But Llandovery were level on 18 minutes when, following a maul, outside centre Warren seized on a missed Newport tackle, collecting from Lee Rees to go over for a try that Ioan Hughes improved.
The Drovers were reduced to 14 men on 25 minutes with back rower Osian Davies escaping with just a yellow card after catching Newport tighthead Nathan Evans with an elbow to the face.
But Newport were unable to capitalise on that numerical advantage, with a couple of knock-ons costing them, while the hosts got a hand in every time they got in behind, with impressive openside flanker Stuart Worrall to the fore.
Rhodri Jones races over in the corner to score the match winning try
Llandovery went back in front three minutes after the re-start after a good finish by inside centre Jones in the corner which, after it went to the TMO, the try was given. Hughes landed with the touchline conversion.
The TMO was then called into action again; first ruling out a second Warren try after a knock on in the build-up on 52 minutes and then on hour Newport thought they had scored again through skipper Ben Roach – only for it to be chalked off for obstruction by Josh Skinner.
Hughes’ late penalty attempt from long range clattered the post and there would be no way through for Newport as the Drovers stood firm and celebrated retaining their title.
