He updated his account profile to read "Footballer for @fortlauderdalecf" and added a snap of himself on the field with the caption, "Follow your dreams."
His doting mum commented, "We are so proud of you Romeo x."
Prior to his contract signing, Romeo celebrated his 19th birthday on September 1 with his family. Of the celebration, a source told PEOPLE, "Romeo was presented with a massive eight-tier birthday cake adorned with family photos, jerseys, soccer balls, and the Inter Miami CF logo representing his father's soccer team. He loved it."
Previously, Romeo's mom Victoria had also discussed Romeo's athletic ambitions during an interview with British Vogue in February. The fashion designer said at the time, "Romeo has been training with the team over here every day, because ultimately that's what he wants to do."
Fort Lauderdale CF (Club de Futbol), is in League One of America's United Soccer League, according to ESPN. It is also the sister team to Inter Miami CF, which is co-owned by David.
Beckham Sr. signed his first professional contract with Manchester United when he was just 17 in 1992. He made his debut for England, aged 21 in 1996, and captained the team for six years, earning 58 caps. He also played for Real Madrid in Spain and the LA Galaxy team in California.