We studied 19 color-banded groups of the cooperatively breeding Superb Fairy-wren (Malurus cyaneus) to determine (1) the contributions of breeding and helper males to antipredator vigilance, (2) whether such vigilance reduces predation risk, and (3) the mechanisms by which it might do so. Time spent as a sentinel (perching and scanning from conspicuous locations within sight of the nest) increased with group size, but successful and depredated nests did not differ significantly in sentinel time, and sentinels did not appear to coordinate their vigilance. Both breeder and helper males acted as sentinels, and both were more vigilant when nests contained nestlings than when they contained eggs. Breeders with helpers spent more time as sentinels than those without helpers. Presence of a sentinel reduced the time feeding adults spent pausing to scan when approaching and leaving the nest. Thus, vigilance could enable a male to detect a predator and decoy it away from the nest site or prevent it from locating the nest by deferring feeding visits of other provisioners, but we could not demonstrate that it reduced nest predation by the major nest predator, the Pied Currawong (Strepera graculina).