Marambionectes (meaning "Marambio Island swimmer") is an extinct genus of weddellonectian elasmosaurid plesiosaur from the Late Cretaceous López de Bertodano Formation of Antarctica.

The Marambionectes holotype specimen, IAA-Pv 752, was discovered in 2018 in sediments of the López de Bertodano Formation (unit 9) near on Marambio (Seymour) Island of James Ross Archipelago, Antarctica.

The specimen is partially articulated and incomplete, consisting of the basioccipital, mandible, some teeth, cervical, pectoral, dorsal, and caudal vertebrae, ribs, an ilium, the right humerus and ulna, and a femur.

The generic name, Marambionectes, combines a reference to Marambio Island, where the fossil material was found, with the Greek word "nectes", meaning "swimmer".

[1] In their phylogenetic analyses, O'Gorman et al. (2024) recovered Marambionectes as a derived member of the elasmosaurid clade Weddellonectia, as the sister taxon to the Aristonectinae.