This study compares seven dimensions of organizational assimilation (OA)—familiarity with coworkers, familiarity with supervisors, recognition, acculturation, involvement, job competency, and role negotiation—into nonprofit, for‐profit, and governmental organizations incorporating the role of similarity of past work experience (magnitude of transition [MoT]). An online survey of 294 employee newcomers (tenures of 3 months or less) revealed differences in OA between those entering nonprofits and those entering for‐profit, and governmental organizations. Compared to newcomers entering for‐profit and governmental organizations, nonprofit newcomers reported higher levels of job competency, involvement, acculturation, and role negotiation. Interactions between organization type and MoT from past work to current roles were examined for effects on OA. When MoT was low, nonprofit newcomers were higher on acculturation and involvement than for‐profit newcomers; governmental newcomers with high MoT were significantly higher on role negotiation than for‐profit newcomers. Theoretical and practical implications for nonprofit organizational management, trainers, and nonprofit newcomers are discussed.