The two roles overlap enough in day-to-day appearance (both coach, both facilitate, both work to improve team effectiveness) that the distinction is easy to blur. The genuine difference is in scope, not in the underlying skill set.
Scope of accountability
A Scrum Master's accountability is explicitly bounded: one or a small number of specific Scrum Teams, and the events, artifacts, and practices defined within the Scrum framework. An Agile Coach's scope is typically broader and less framework-bound: multiple teams, often spanning an entire department or organization, frequently working across different frameworks rather than being tied to one.
Depth versus breadth
A Scrum Master goes deep with a small number of teams over a sustained period, building close, trust-based relationships from being embedded through many sprints. An Agile Coach typically goes broad, working with more teams, but with less day-to-day embedded presence in any single one.
Organizational versus team-level focus
A Scrum Master's obstacle-removal work is fundamentally in service of a specific team's effectiveness. An Agile Coach more often works directly on organizational-level obstacles (structural issues, cross-team coordination, leadership behavior) that no single team's Scrum Master has the mandate to address alone.
Framework flexibility
A Scrum Master's expertise is specifically grounded in Scrum. An Agile Coach typically needs broader fluency: comfortable helping a Kanban team as readily as a Scrum team, and often responsible for helping an organization choose which framework actually fits its context.
Where the confusion comes from in practice
Job titles in the market don't consistently reflect this distinction. The titles are a weaker signal than the actual described scope of accountability, which is worth checking directly rather than assuming from the job title alone.
When an organization needs which
A single team or a small handful of teams new to Scrum typically need a genuine Scrum Master, deeply embedded. An organization undertaking broader transformation typically needs Agile Coaching at the organizational level, in addition to, not instead of, Scrum Masters at the team level. The two roles are complementary, and organizations that only invest in one tend to see the gap the other would have filled.