Voter registration among young people is significantly lower and they turn out less than older voters. Moreover, they are hard to reach with conventional registration methods such as canvassing and direct mail. As of late there have been large-scale attempts to register and mobilise young voters via social media campaigns on various platforms, both by partisan and non-partisan actors. However, there is a lot of scepticism regarding whether social media campaigns are effective. The experimental literature suggests that the effect of social media ads on persuasion and mobilisation are positive but small (Bond 2012, Hager 2019). In this field experiment, we worked with a non-partisan organisation to test if their social media registration drive on Instagram and Snapchat was effective at registering young people to vote in the 2019 UK General Election. In a large-scale RCT – the first of its kind - we assigned 879 postcode sectors located within 40 parliamentary constituencies to four groups: control, one group that received voter registration video ads. These messages were targeted towards young people aged 18-35 years. We collected voter registration at the polling district level (polling stations can perfectly be matched to postcode sectors) and from official voter registers to test whether social media campaigns targeted towards young people can increase voter registration and turnout.