Newcastle Falcons have signed New Zealand-born former Ireland international front-row forward from Irish province Pro 14 side Ulster.
The 30-year-old three-times capped prop has signed with immediate effect.
"Rodney has been a proven performer at a high level for a number of years now and he will definitely add to what we already have here," said Falcons director of rugby Dean Richards.
"I'm pretty stoked that Dean Richards came after me," said Ah You.
"I've played at Newcastle a couple of times with Connacht. I've watched get a couple of really good wins recently in the Champions Cup and there are a lot of good things going on around the place.
"I can play on both sides of the front row if needed. Tight-head is where I have been playing mainly but I can jump over if the coaches need me to."
Ah You's first involvement could come as early as Friday night when the Falcons meet Bath in the Premiership at Kingston Park.