We report the discovery of a low-mass companion to HR 3549, an A0V star surrounded by a debris disk with a warm excess detected by WISE at 22 μm (10σ significance). We imaged HR 3549 B in the L band with NAOSCONICA, the adaptive optics infrared camera of the Very Large Telescope, in January 2013 and confirmed its common proper motion in 2015 January. The companion is at a projected separation of ;80 AU and position angle of ;157°, so it is orbiting well beyond the warm disk inner edge of r > 10 AU. Our age estimate for this system corresponds to a companion mass in the range 15–80 MJ, spanning the brown dwarf regime, and so HR 3549 B is another recent addition to the growing list of brown dwarf desert objects with extreme mass ratios. The simultaneous presence of a warm disk and a brown dwarf around HR 3549 provides interesting empirical constraints on models of the formation of substellar companions.