The multiyear deal, announced by league officials on Monday, comes just months after the Baltimore-based company launched its first line of athletic footwear at the NFL Draft in April. It already supplies moisture-wicking shirts for professional and college players, in addition to a full line of apparel for consumers.
Among other benefits, the deal allows the company to use the official NFL logo in advertising and marketing, while its own brand will no longer have to be taped over by players already wearing Under Armour cleats -- including A.J. Hawk of the Green Bay Packers and Vernon Davis of the San Francisco 49ers, among others.
The league also issued warrants to buy up to 480,000 of the Under Armour's Class A shares, according to a statement released by the company.
"Now we have an official presence on Sundays with some of the best players in the world," Under Armour founder and CEO Kevin Plank said in a statement.
In announcing the deal, Roger Goodell, the NFL's executive vice president, described Under Armour as an "exciting, fast-growing company with a strong history in football."
Plank, a former special-teams captain for the University of Maryland, called the partnership the "next logical chapter" for the company, which in June reported an increase in second-quarter net revenue of 63.3% to $80 million. It expects annual net revenue to reach $400 million, a 42% gain over 2005.
Under Armour was founded in 1996, and in 2003 ranked No. 2 on Inc. magazine's annual list of the nation's fastest growing private companies. At the time, the company had 180 employees and $50.7 million in annual revenue, posting a growth rate of 12,753% over the previous three years.