We conduct a natural field experiment with a major European party to test whether giving party supporters more voice increases their engagement in the party's electoral campaign. In the experiment, the party asked a random subset of supporters for their opinions on the importance of different policy areas. Giving supporters opportunities to voice their opinions increases their engagement in the campaign as measured using behavioral data from the party's smartphone application. Survey data reveals that giving voice also increases other margins of campaign effort as well as perceived voice. Our evidence highlights the importance of voice for increasing political engagement.