The 34-year-old right back made 451 appearances for Real Madrid, where he claimed 27 major trophies, and is one of only five players to have won Europe's elite club competition six times.
Carvajal, who also spent a season at Bayer Leverkusen, earned 51 caps for Spain, winning the European Championship in 2024 and the Nations League in 2023.
Getafe, who are 14th in LaLiga with eight points from eight games, are scheduled to visit Real Madrid in January, when Carvajal could face his former club for the first time.