Large-scale urban conflagrations in informal settlements are a frequent global event, however there is a lack of experimental research and knowledge within literature on how informal settlements fires spread to support local or national intervention strategies. This paper, therefore, presents results and analysis of a full-scale fire spread experiment of a mock 20 dwelling test settlement with a 4 by 5 layout aimed at understanding settlement-scale fire spread behaviour. A “fire line” scenario was created by simultaneously igniting four dwellings in a row, and then allowing the fire to propagate through the settlement to replicate fire disasters involving large numbers of homes. Results highlight the critical hazard posed by the close proximity of neighbouring dwellings (1–2 m), with wind playing a primary role in directing and driving the spread process. Even with a relatively mild wind speed of 15–25 km/h, the fire spread through the entire mock settlement within a mere 5 min. Following ignition of a given dwelling, flashover is reached very quickly, with the temperatures reaching more than 1000°C within 1 min, and downwind neighbour structures igniting less than a minute thereafter. The results suggest that multi-dwelling effects are not dominant in these types of fires, but may become meaningful at a larger scale when branding and topography play a role. Findings show that on a global scale fire behaviour is analogous to a wildfire with a continuous fire front moving through an area, although individual dwellings still do follow the distinct phases of enclosure fires, except that collapse occurs more rapidly than in formal structures. This experiment represents one of the larger urban fire tests conducted to date, and the largest informal settlement fire experiment.