Swarbrick joined LBC, the London-based radio station owned by Global Radio, in June 2012 as chief correspondent and presenter. He was named National Journalist of the Year in 2014 Radio Academy Awards.
Prior to joining LBC, Swarbrick worked for the BBC as a radio producer and presenter at BBC Radio Oxford.
Swarbrick announced his new role on social media, tweeting:
James Rea, managing editor of LBC, said: "Tom has made an enormous contribution to LBC over the last five years, from a rookie reporter to chief correspondent and presenter. He leaves with our huge thanks and best wishes."
Swarbrick is among a number of former journalists to join May’s team since she became PM in July. This includes former Mail on Sunday journalist Liz Sanderson and May's chief of staff Fiona Hill, a former reporter for Sky and The Scotsman who had worked for her for a number of years.
May’s comms operation is headed by Katie Perrior, co-director of iNHouse Communications, who ran Boris Johnson’s PR during his 2008 bid to become London Mayor, as well as his successful 2012 re-election campaign.