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Many operations research problems in project management, manufacturing, and elsewhere require the generation of specified sets of activity networks for purposes of testing proposed solution approaches. To date, single-network generators have been used for the resource-constrained project scheduling problem (RCPSP). Since the first single-network generator was proposed in 1993, several advances have been reported in the literature. However, these generators create only one network or project at a time; they cannot generate multi-project problems to desired specifications. This paper presents the first multinetwork problem generator. It is especially useful for investigating the resource-constrained multi-project scheduling problem (RCMPSP), where a controlled set of multi-project test problems is crucial for analyzing the performance of solution methods. In addition to the usual single-project characteristics handled by existing network generators—such as network size, shape, and complexity, activity duration, resource types, and resource usage—the proposed generator produces multi-project portfolios with controlled resource distributions and amounts of resource contention. To enable the generation of networks with desired levels of complexity, we also develop several theoretical insights on network structure in terms of tiering. Finally, we statistically analyze 12,320 generated test problems and conclude that the generator quickly produces “near-strongly random” problems. Fully strongly random networks are possible but increase computational intensity.