A total of 22 teams contested the league, including 15 sides retained from the 2019–20 season, three relegated from the 2019–20 La Liga, and four promoted from the 2019–20 Segunda División B.
On 12 July 2020, Cádiz became the first team to be promoted to La Liga, ending a 14-year run in the lower divisions, seven of which were spent in Segunda División B, following Oviedo's 1−0 win against Zaragoza.
[3] The final team to achieve promotion were play-off winners Elche after defeating Girona 1−0 on aggregate, they return to La Liga after a five-year absence, with one of those seasons spent in Segunda División B.
[9] On 20 July 2020, the final round of the 2019–20 season, Numancia and Deportivo de La Coruña were relegated after Albacete won 1–0 away to Cádiz.
They were set to play in the Segunda División for the first time in their history, and to bring back professional football to La Rioja 20 years after the relegation of former CD Logroñés.