Born November 19, 1996, in San Marcos, California, Federico Anthony Warner grew up in a diverse household—Mexican American from his mother Laura's side and African and Panamanian from his father Fred's side. Raised by his single mother alongside two siblings after his parents separated when he was a toddler, Warner credits football with providing structure and community during his formative years. At Mission Hills High School, he became a starter his junior year and earned All-San Diego Section Defensive Player of the Year honors, catching the attention of BYU coaches through a fellow church member who sent his highlight reel to recruiters.

Warner played at BYU from 2014 to 2017, developing into a three-year starter who recorded 264 total tackles and seven interceptions, including two returned for touchdowns that tied him for second in school history among linebackers with Kyle Van Noy. His impressive Senior Bowl performance in January 2018 elevated his draft stock, leading the San Francisco 49ers to select him in the third round with the seventieth overall pick.

Head coach Kyle Shanahan immediately named Warner the starting middle linebacker for his rookie season. Warner's exceptional combination of elite coverage skills, sideline-to-sideline speed, and football intelligence transformed the 49ers' defense. November 10, 2019, showcased his versatility when he recorded ten tackles, sacked Russell Wilson twice, and forced a fumble recovered by teammate DeForest Buckner for a touchdown in an overtime thriller against Seattle. Six weeks later against the Rams, he intercepted Jared Goff and returned it 46 yards for his first NFL touchdown in a 34-31 victory. His defining moment came September 29, 2024, when he returned an interception 45 yards for a touchdown against New England, becoming the first player in 49ers franchise history to record ten career sacks and ten career interceptions.

Through eight seasons, Warner has compiled 948 total tackles (ranking second in franchise history behind Hall of Famer Patrick Willis), ten sacks, seventeen forced fumbles, and ten interceptions while leading the 49ers in tackles every year of his career. His 28 passes defensed from 2022 to 2024 rank most among NFL linebackers during that span. Warner has earned four First-team All-Pro selections (2020, 2022-2024) and four Pro Bowl nominations, with May 2025 bringing a three-year, $63 million contract extension making him the highest-paid linebacker in NFL history.

Warner graduated from BYU in December 2017 with a degree in exercise and wellness and married former The Bachelor contestant Sydney Hightower in June 2022. He collaborates with Bay Area law firm Venardi Zurada on an annual Thanksgiving Food Drive in Walnut Creek that collected 1,388 pounds of food in 2024, providing approximately 1,157 meals for families in need. Warner partners with Nike and the Hispanic Scholarship Fund to provide Latino students with scholarships and career readiness programs while supporting mental health awareness initiatives through CASSY and raising awareness for chronic obstructive pulmonary disease as his My Cause My Cleats charity.