Extremist groups frequently leverage online spaces in recruitment and organization efforts. This research assessed how basic psychological need expression among users of extremist chatrooms was related to forum engagement and hate term use. ∼20,000,000 posts from ∼90,000 users on 233 Discord chatrooms were scraped from a publicly available database. Using a natural language processing approach, users received scores on three needs based on semantic similarity between posts and needs measures. Multilevel models assessed associations between need expression and number of posts, length of chatroom activity, and hate term use. Results indicated that users who expressed more autonomy and competence were more engaged and used hate terms less. Smaller and less robust effects were observed for relatedness. Results suggest that basic psychological needs are associated with behaviors in extremist chatrooms and that the decades of research on basic psychological needs can be leveraged to better understand radicalization and extremist behaviors.