McLoughlin has been deputy head of policy and head of external relations at the IoD since 2014, leading on areas such as entrepreneurship and the digital economy. It is understood he was given leave from the IoD to work on May's leadership campaign.
He'll pick up much of the work of Dan Korski who left Number 10 after David Cameron's resignation, having coordinated much of the business community's support for the Remain campaign.
Since she got the keys to Number 10, Theresa May has put big business in her sights with pledges to clamp down on excessive pay - and it's likely McLoughlin will play a key role in liaising with the business community on the PM's reform agenda.
“Jimmy has done great work making the IoD more open to entrepreneurs, helping The99, our membership scheme for younger businesses, recently hit 1,000 members," said Simon Walker, director general of the IoD
"He has led our work on giving more people a chance to invest in growing companies, and I’m sure he will be a champion for start-ups and innovation in government. We will be very sorry to see him go, but wish him all the best.”