The six-time All-Star posted about the development Monday on social media.
"Mission accomplished," Cruz wrote in the caption for an Instagram photo. "Next stop: Registering to vote."
Cruz held a certificate and a miniature American flag while sporting a suit and smiling for a photo. He also rocked some patriotic American flag-themed shoes.
The photo had more than 23,000 likes and several comments from fellow players as of Tuesday morning.
Cruz, 38, was born in Las Matas de Santa Cruz, Dominican Republic. He hit .256 this season with 37 home runs and 97 RBIs in 144 games for the Mariners. Cruz broke into Major League Baseball on Sept. 17, 2005 with the Milwaukee Brewers.
For his career, he owns a .274 average and has 360 home runs over 14 seasons for the Brewers, Texas Rangers and Mariners. He made $14.2 million this season and is a free agent this offseason.