District One was one of the five constituencies (Spanish: circunscripciones) represented in the Regional Assembly of Murcia, the regional legislature of the Region of Murcia. The constituency elected seven deputies. It comprised the municipalities of Lorca, Aguilas, Puerto Lumbreras, Totana, Alhama de Murcia, Librilla, Aledo and Mazarrón. The electoral system used the D'Hondt method and a closed-list proportional representation, with a minimum threshold of five percent regionally.