The colossal squid (Mesonychoteuthis hamiltoni) is the world's largest invertebrate and its large size and some unique morphological characters have fuelled speculation that it is an aggressive top predator in the circum-Antarctic Southern Ocean. Here, we present estimates on the metabolic and energetic demands of this cold-water deep-sea giant. The estimated mass-specific routine metabolic rate for the colossal squid at 1.5°C was 0.036 µmol O2 h−1 g−1 and the projected daily energy consumption (45.1 kcal day−1) was almost constant as a function of depth in the nearly isothermal Antarctic waters. Our findings also indicate the squid shows a slow pace of life linked with very low prey requirements (only 0.03 kg of prey per day). We argue that the colossal squid is not a voracious predator capable of high-speed predator–prey interactions. It is, rather, an ambush or sit-and-float predator that uses the hooks on its arms and tentacles to ensnare prey that unwittingly approach.