A strong second half for the home side. Three penalties plus a try from Hudson Tonga'uiha killed the game off.
The Pirates didn't give up and pulled a late try back from Ryan Storer, but this was cancelled out by Jack Moates.
So defeat on the night and on aggregate secures London Welsh the Championship trophy.
Welsh are now expected to take legal action over the RFU's ruling that they are not eligible for promotion to the Premiership.
More top news
It's going to be unsettled with yet more rain on the horizon
Hundreds of women have gathered at Westminster to protest the government's decision to delay the age they can take their state pension.
Police dog Sasha's eight offspring need to be named before they go to their puppy walkers in a few weeks - but there's a catch.