Private landholders’ contributions to biodiversity conservation are critical in landscapes with insufficient formal conservation reserves, as is the case in Australia's tropical savannas. This study reports results from a discrete choice experiment conducted with pastoralists and graziers across northern Australia. The experiment was designed to explore the willingness of pastoralists and graziers to sign up to voluntary biodiversity conservation contracts. Understanding preferences for contractual attributes and preference heterogeneity were additional objectives. Such knowledge can increase effectiveness and efficiency of conservation programs by informing contract design, negotiation and administration. Random parameter logit modelling showed that of contract attributes, conservation requirement, stewardship payment, contract duration and flexibility in contract conditions significantly influenced choices. Land productivity was a significant factor as were attitudes. There was significant heterogeneity of preferences for all contract attributes. Models were run for best–worst scaling responses and the first preferences subset, with the latter model deemed superior. Latent class modelling distinguished four classes of decision‐makers and illustrated different decision heuristics. Conservation investment strategies, which offer farmers contract options that meet biodiversity requirements while accommodating heterogeneous attribute preferences, are likely to lead to increased participation rates. Complementary suasion efforts are also required which espouse the benefits that pastoralists derive from biodiversity and participation in voluntary conservation contracts.