Mycobacterium (M.) tuberculosis mostly spreads from active tuberculosis (TB) patients to human contacts, although human-to-animal and animal-to-human transmission has been described. Here, we present a rare case of rifampicin-resistant tuberculosis (RR-TB) transmission from a companion dog to its owner, highlighting the zoonotic potential of the pathogen. Namely, a 37-year-old Croatian man was diagnosed with RR-TB, with whole-genome sequencing analysis revealing a close genetic link to the strain isolated from his dog, which had died of miliary TB six years earlier. This case emphasizes the complexity of TB transmission dynamics, particularly involving companion animals, and underlines the importance of integrated “One Health” approaches for TB control. Awareness of zoonotic TB risks is essential for the early detection and prevention of cross-species transmission, especially in vulnerable populations and households with close human–animal contact.