The current deal with Pinnacle Insurance runs out in May after a six-year association with the club.
Forest Chief Executive Mark Arthur told the club's website: "We are delighted to be linking up with Capital One in a sponsorship deal that reflects the ambitions of both organisations.
"We set out two years ago to put the Nottingham back into Nottingham Forest and I firmly believe our partnership with another major brand from the city will help us achieve that goal."
The Capital One logo will be on the team strip, training kit and around The City Ground. Capital One will also be involved in local community projects together with Nottingham Forest Football Club.
The deal is thought to be worth just under £2m per year. Capital One is a top ten credit card issuer in the United States and has 47 million customers worldwide.