He played college football at Florida and was selected by the New Orleans Saints in the fourth round of the 2019 NFL draft.

On December 31, 2017, he announced he changed his last name to Gardner-Johnson in honor of his stepfather, Brian Johnson.

[1] In both 2020 and 2023, Gardner-Johnson posted his intention to legally change his name to Ceedy Duce on Instagram.

[8] On November 26, 2018, Gardner-Johnson announced that he would forgo his final year of eligibility and declare for the 2019 NFL draft.

[13] Throughout training camp, Gardner-Johnson competed for a role as a backup safety against Chris Banjo, Saquan Hampton, J. T. Gray, and Terrell Williams.

[15] Head coach Sean Payton chose Gardner-Johnson to be the backup strong safety to start the season, behind starter Vonn Bell.

[16] In September 9, 2019, Gardner-Johnson made his professional regular season debut in the New Orleans Saints' home-opener against the Houston Texans, but was limited to one tackle in their 30–28 victory.

[17] In a Week 13 game against the Atlanta Falcons on Thanksgiving Day, Gardner-Johnson recorded his first career interception off a pass thrown by Matt Ryan in the 26–18 win.

[18] On December 16, 2019, Gardner-Johnson had his first start at strong safety and recorded eight combined tackles (six solo) and forced a fumble by wide receiver Kalif Raymond which he recovered during the 34–7 win against the Indianapolis Colts.

[19] He started the last three games at strong safety in place of Vonn Bell who was inactive due to a knee sprain.

[27] In Week 10 against the San Francisco 49ers, Gardner-Johnson recorded his first career sack on quarterback Nick Mullens during the 27–13 win.

[28][29] In Week 12 against the Denver Broncos, Gardner-Johnson intercepted a pass thrown by wide receiver Kendall Hinton during the 31–3 win.

In the Super Bowl, Gardner-Johnson recorded four tackles in the Eagles 38–35 loss to the Kansas City Chiefs.

[48][13] Gardner-Johnson suffered a non-contact leg injury during the start of Lions training camp on July 23, 2023.

Despite fears of a potentially season-ending ligament injury, it was announced the next day after an MRI that Gardner-Johnson avoided structural damage and was "day-to-day" in his recovery.

[54] In the 2025 NFL Playoffs, Gardner-Johnson and rest of the Eagles' defense played well enroute to a 40–22 victory against the Kansas City Chiefs in Super Bowl LIX.