Topps will sell its sports card business to Fanatics, a rival.

Topps, the business that put Bazooka bubble gum together with baseball cards more than half a century ago, now belongs to a fast-growing sports memorabilia empire that nearly knocked Topps out of the baseball-card game.

On Tuesday, Topps announced that it had sold its sports card business to Fanatics, a multibillion-dollar, 10-year-old company whose licensing business was built on sports fandom, technology and networking. The deal values Topps’s sports and entertainment division at slightly more than $500 million, according to people with knowledge of the situation, speaking on the condition of anonymity because the information is confidential.

Topps had previously announced a deal to go public. But in August, the company was blindsided when it lost its licensing agreement with Major League Baseball and the Major League Baseball Players Association to Fanatics, putting its future in doubt. Fanatics and Topps began discussing the acquisition of Topps’s card business roughly a month after Topps lost the baseball contract, a person familiar with the situation said.

“Topps is synonymous with card collecting — it’s the primary brand that people think of when you think of baseball cards and sports cards,” said Chris Ivy, the director of sports auctions for Heritage Auctions. “So the fact that they will be continuing going forward, I think is a great thing both for collectors and the industry as a whole.”

The Topps deal mirrors Fanatics’s purchase of the apparel company Majestic, which it acquired after winning the rights to make major-league uniforms, contracts that Majestic had previously won. The deal announced on Tuesday also underscores the breadth of businesses Fanatics has built, aiming to grow beyond ticketing and television, both of which are difficult to expand rapidly. Leagues are looking to new places for revenue, including advertisements on jerseys and legalized sports gambling — and trading card licensing agreements.

The Topps playing card business may not immediately transform under its new ownership. Topps cards will still carry the Topps logo, and the division’s roughly 350 employees will work for the Topps brand independently within Fanatics. But longer term, Fanatics hopes to create for Topps the digital agility that helped transform its licensed apparel business, which is set up to respond quickly to quick shifts in the popularity of an athlete.

Fanatics started its playing card business last year, around the same time it struck deals with unions for N.F.L. and N.B.A. players to produce football and…