Bacteria live in complex polymicrobial environments where they are constantly competing for space and resources. To dominate in these environments, many Gram-negative bacteria use a potent nanoweapon termed the type VI secretion system (T6SS) that delivers deadly toxins directly into adjacent cells. A class of T6SS toxins, called rearrangement hotspot (Rhs) effectors, are known to interact with T6SS structural machinery for delivery, but the precise interactions and activation of these toxins is poorly defined. We characterised a novel T6SS Rhs effector (Tse15) from the multidrug-resistant hospital pathogen Acinetobacter baumannii. We show that prior to delivery, Tse15 undergoes auto-processing into three separate domains that remain associated in solution. The 1.8Å cryoEM structure of Tse15 shows the central Rhs domain forms a triple layered β-cocoon with an N-terminal a-helical domain that sits outside the cocoon and an unfolded C-terminal toxin domain located inside the β-cocoon, physically protecting the host cell from self-intoxication. This is the first structure of a T6SS effector from A. baumannii, and the only Rhs effector structure that has the full-length protein resolved. For the first time, proteomic analyses showed that the N-terminal and toxin domains, but not the Rhs β-cocoon, are delivered outside of the host cell, suggesting a novel mechanism for Rhs toxin delivery and activation. Our findings suggest that toxin delivery requires an interaction between the N-terminal and toxin domains, with the N-terminal acting as an internal chaperone to mediate tethering of the toxin to the T6SS machinery. Strikingly, conservation of the N-terminal domain in other Gram-negative bacteria suggests this represents a universal mechanism for T6SS toxin delivery. Defining T6SS toxin delivery allows for the design of anti-T6SS therapeutics, and for artificial payloads to be delivered by this nanomachine.