O'Mara's campaign focused on disabled people's rights, protecting public services and on his personal background in Sheffield. His campaign benefited from a national surge in the Labour vote and from university students in the constituency. It was claimed Nick Clegg was thought to be too anti-Brexit by voters, although Sheffield Hallam was estimated to have voted Remain in the 2016 European Union referendum and O'Mara supports Remain as well. A Progress and Momentum supporter, O'Mara was backed by them during the election campaign. He won the seat with a majority of 2,125 votes, overturning Clegg's previous majority of 2,353 votes. The result was considered one of the most important seat changes of the night; O'Mara had not expected to win the seat. His acceptance speech called for politicians to do more to stand up for disabled people.