In the fashion industry, the effectiveness of influencer marketing, known as “opinion leaders,” via Instagram remains little known to brand managers and scholars despite the frequent use of such a communication strategy by companies in recent years. Likewise, to the best of our knowledge, no study has jointly addressed the determinants of opinion leadership, specifically source and content factors. This article aims to examine the determinants and impact of opinion leadership on Instagram female millennial followers' intention to adopt fashion recommendations. Data was taken from a survey carried out on 280 followers of a fashion Instagram account. Web‐administered questionnaires were used to collect the data, which was processed using an exploratory factor analysis and a structural equation modeling. The findings indicated that perceived credibility, psychological closeness to the influencer, and perceived originality of content affected respectively opinion leadership. Thus, opinion leadership affected positively consumer's intention to follow recommendations. Moreover, it turned out that perceived product‐influencer congruence had no moderating effect on the link between opinion leadership and the followers' intention to follow recommendations. Then, this study contributes to a better understanding of the determinants of opinion leadership and the impact of opinion leaders on promoting fashion products.