The Brazilian winger completed his switch to London after a £25m deal was agreed with PSG.
After featuring just six times for the Parisians this season, it was time for the 25-year-old to find a fresh start.
"I'm so, so happy," Moura said. "It's a new chapter in my life, a new challenge for me.
"I've joined a big club with big players and I look forward to playing and helping the team.
"I can play in the Champions League, which is a big objective for me and to make new friends is always a pleasure.
"I will give my best for this club. I think we have a lot of quality and I think we can win big things."
Moura has been capped 34 times by Brazil and he's hopeful the move will give him a chance to make the Selecao World Cup squad.