This article examines a multi-year study of a client-based, critical service-learning project embedded in a Professional Writing course at a Jesuit Catholic university. Drawing on surveys and interviews with students across six course sections, the study explores how students perceived service learning, which aspects of the project most shaped their learning, and how the university's mission informed their understanding of service and professionalism. Findings reveal that while students often entered the course with conventional assumptions about service as charity and professionalism as formality, many came to adopt a more relational, justice-oriented view of professional communication. By engaging with real clients—many of whom face structural inequities—students encountered the human realities behind workplace writing and began to see professionalism as a flexible, context-responsive ethic grounded in care and reciprocity. This article proposes the concept of justice-oriented professionalism as a reimagined model for technical and professional communication, one aligned with critical pedagogy, social justice, and relational responsiveness.