The 35-year-old Somalia-born Briton decided to quit the track after last year's world championships and focus solely on the marathon, AFP reported.
It paid off – he set a new European mark of 2hrs 05mins 11secs when winning the prestigious Chicago Marathon in October.
Farah, a quadruple Olympic champion having achieved the distance double of 5000m and 10000m in 2012 and 2016, said he was looking forward to pitting his wits against the traditionally strong field the race attracts.
"I'm delighted to confirm I'll be returning to race the London Marathon again next year," Farah said in a statement issued by the organizers of the April 28 race.
"I've often said how racing in London is very special to me and the London Marathon gives me the chance to run in front of my fans, on my home roads, where the atmosphere is like nothing else."
Farah, also a six-time world track champion, said he is delighted with the progress he has made this year although his European mark is some way off the world best set in Berlin this year by Kenyan Eliud Kipchoge of 2hr 1min 39sec.
"I feel I have made great strides in the past year, finishing third in London in April, and winning my first major marathon in Chicago in October," said Farah.
"That and breaking both the British and European records has given me the confidence that I can compete against the best marathon runners in the world.
"London always puts together a world-class field and I expect that will be exactly the same in 2019 and I can't wait for the challenge."