The 31-year-old back-rower arrives at Franklin's Gardens after a year at French club Bourgoin, and he is delighted with the move.
"It's great to be at a big club, certainly the biggest club that I've ever been at," said Oakley. "I'm relishing the chance to do well here.
"Unfortunately Bourgoin's financial situation meant that things didn't go as well as I wanted in France, but Saints gave me a ring. Things went well and here I am!
"I think I'm coming to Northampton as a more rounded player from my time in France. I had to take a lot more onto my own back and become a lot more professional, rather than have it being forced on me, and I had to learn to communicate effectively in a different way."
Oakley added that his experience in France will help him at Saints.
"I'm glad I got away from the Premiership for a year; it was good to experience a different culture," he said.
"So I feel like I'm here refreshed as a player and ready to make the most of my opportunity.
"The Saints' style of play suits my game and I hope I'll do well here."
Oakley has won international honours with Wales and played for Newport Gwent Dragons for three years.