The development of a portfolio of COVID-19 vaccines to vaccinate the global population remains an urgent public health imperative1. Here we demonstrate the capacity of a subunit vaccine, comprising the SARS-CoV-2 spike receptor binding domain displayed on a protein nanoparticle (RBD-NP), to stimulate robust and durable neutralizing antibody (nAb) responses and protection against SARS-CoV-2 in non-human primates. We evaluated five adjuvants including Essai O/W 1849101, a squalene-in-water emulsion; AS03, an alpha-tocopherol-containing oil-in-water emulsion; AS37, a TLR-7 agonist adsorbed to Alum; CpG1018-Alum, a TLR-9 agonist formulated in Alum; and Alum. RBD-NP immunization with AS03, CpG1018-Alum, AS37 or Alum induced substantial nAb and CD4 T cell responses, and conferred protection against SARS-CoV-2 infection in the pharynges, nares and bronchoalveolar lavage. Live-virus nAb response was maintained up to 180 days post-vaccination with RBD/AS03, and correlated with protection. RBD-NP immunization cross-neutralized the B.1.1.7 variant efficiently but showed a reduced response against the B.1.351 variant. While RBD-NP/AS03 demonstrated a 4.5-fold reduction in neutralization of B.1.351, the RBD-NP/AS37 group showed a 16-fold reduction, suggesting differences in the breadth of the nAb response induced by these adjuvants. Furthermore, RBD-NP/AS03 was as immunogenic as a prefusion stabilized Spike immunogen (Hexapro) adjuvanted with AS03. These data highlight the efficacy of the adjuvanted RBD-NP vaccine in promoting protective immunity against SARS-CoV-2, and have paved the way for the clinical evaluation of this vaccine in Phase I/II clinical trials (NCT04742738 and NCT04750343).