It is expected to begin by bringing its Hot Boxes and salads to London’s Paddington and Liverpool Street stations later this year.
The group – which saw profits jump to £2.26m in 2015 – has partnered with travel food specialist SSP, which operates restaurants in Stansted and Heathrow airport.
John Vincent, co-founder of Leon, said: “When we started we imagined what fast food would be like in heaven – fast, fresh and naturally flavourful. And just like traditional fast food, we aim to be where people need and want us – on busy high streets, in airports and in train stations.”
Leon was founded by John Vincent and Henry Dimbleby – the son of broadcaster David Dimbleby – in 2004.
It currently operates 35 stores in London, Birmingham and transport hubs around the UK.
The group’s first restaurants in Scotland and Amsterdam are set to launch this summer, ahead of a planned Florida site in 2017.
It comes after Leon secured a £11.5m investment from HSBC last October to enable it to grow the business both in the UK and internationally.
Vincent said: “This partnership with SSP in UK train stations means that together we can bring naturally fast food to even more busy people across the UK."