How do marketing campaigns encourage a majority group of consumers to support a minority group of consumers’ opinion? Why do consumers change their opinions? Why do consumers do what they do? Conversion theory addresses a simultaneous majority and minority influence on consumer behaviour. Whilst conversion theory is applied to various disciplines, there is a gap in literature on conversion theory as applied to the marketing discipline. This paper focuses on conversion theory in marketing and contributes by introducing three new propositions to marketing literature, namely, (1) marketing campaigns can convert the majority opinion to support the minority opinion privately and/or publicly when portraying ‘consistency’, (2) marketing campaigns can convert the majority opinion to support the minority opinion privately and/or publicly when portraying a style of thinking that encourages discussion amongst the majority, and (3) marketing campaigns can convert the majority opinion to support the minority opinion privately and/or publicly when the majority identifies themselves with the message of the marketing campaign.