In recent years, influencer marketing has emerged as a powerful tool for brands to create connections with their target audiences. Naturally, many companies have leaned on human influencers, but the increasing popularity of pet influencers (e.g., dogs and cats) represents a new avenue for brand promotion. This research asks the question: Why and when are pet influencers preferrable to their human counterparts in terms of boosting engagement and purchase intention? Across six experimental studies (N = 1166), we demonstrate that pet influencers lead to higher engagement with the promoted content and willingness to buy the advertised product (Study 1) because they are seen as more credible than human influencers (Study 2). Pet influencers are perceived as cuter, which in turn positively affects their credibility (Study 3). Specifically, whimsicality is the cuteness dimension that explains their greater credibility (Study 4). These effects are stronger when the promoted product is pet‐related (Study 5) and apply regardless of whether people own a pet (Studies 3–5). Finally, a clear cuteness manipulation supports the causal relationship between cuteness and credibility (Study 6). These findings affirm that pet influencers shape individuals' responses to promotional social media posts, enhance the field's understanding of the mechanisms that underlie influencer marketing effectiveness, and clarify how to implement more influential social media campaigns.