<p>Minority opinions often generate crucial ideas and knowledge, but it is more challenging to be a minority opinion holder in an ingroup (disagreeing with members of one’s own group) than in an outgroup (disagreeing with members of other groups). This paper extends the group decision-making, knowledge sharing, and minority influence literatures by exploring a psychological condition under which ingroup minority opinion holders can be influential in diverse decision-making groups. Across two experiments, activating group attachment security (vs. neutral condition) increased minority opinion holders’ task focus and the persuasiveness of their expressed dissenting opinions (Study 1), and increased majority members’ willingness to use that dissent while these authentic texts also differed in argument quality (Study 2). Although the predicted omnibus attachment-by-social-category (secure vs. neutral × ingroup vs. outgroup) interactions were generally non-significant, exploratory simple-effects comparisons suggested these effects were more notable among ingroup minorities. These findings suggest that group attachment security can help minority opinion holders be influential in decision-making groups that represent diverse social categories.</p>