Integrating theories from relationship management, organizational socialization, and leadership communication, the current study examines how an essential component of internal communication—leaders’ use of motivating language—can facilitate newcomers’ socialization, strengthen their relationship with the organization, and promote psychological well-being over time. Our findings, based on a two-wave longitudinal survey of 390 full-time employees in the United States, demonstrate that leaders who use motivating language, especially by providing guidance and creating a sense of purpose, facilitate new employees’ understanding of their roles and adaptation to the organization. The use of motivating language also has long-term benefits on newcomers’ relationship quality with the organization and their psychological well-being. We conclude by discussing the implications of our results for communication professionals designing onboarding programs and coaching organizational leaders on effective communication with new hires.