Double Olympic champion Mo Farah will run half of this year's Virgin London Marathon before making his debut over the full distance on the streets of the capital in 2014.
Farah will start with the elite men's field on April 21 and run to halfway, alongside the likes of marathon world record holder Patrick Makau, Olympic champion Stephen Kiprotich and world champion Abel Kirui.
The 29-year-old, who won Olympic gold over 10,000 and 5,000 metres in London last year, has always said he would eventually move up to the marathon, with his coach Alberto Salazar suggesting Farah could even target a marathon and 10,000m double at the Rio Olympics in 2016.
Farah, who was competing over 3,000m at the British Athletics Grand Prix today before switching to a half-marathon in New Orleans next weekend, said: "As a young boy growing up in London it has always been my ambition to run the London Marathon.
"I won the Mini Marathon when I was younger and have watched the race every year for as long as I can remember.
"I will make my marathon debut in the 2014 London Marathon but will run the 2013 race to halfway as part of my preparation for 2014. It will allow me to understand the course and the systems I will need when I run the full distance.
"To run as the double Olympic champion makes it even more special. Dave Bedford (former race director) and the London Marathon have always been there for me and it will be my pleasure to run my first marathon in London."
Farah made his half-marathon debut in 2011 when he won in New York in 60 minutes 23 seconds, a British record.
London Marathon race director Hugh Brasher said: "We are delighted that Mo wants to run with our elite runners this year.
"We have been following and supporting Mo's career since he first won the Mini London Marathon 15 years ago and are full of anticipation for his marathon debut in 2014.
"Hopefully, his experience of the race, the route and the unique atmosphere of the London Marathon will stand him in good stead when he takes on the full race next year.
"We are sure he will gain some valuable insights and come back fully prepared for the challenge."
