As well as monthly car packs, the open-world racer will also receive larger content packs to help keep the release evergreen.
The first expansion will be available on December 18, design director Ralph Fulton told Digital Spy.
While no details were provided on what each expansion will add, it's expected to offer more substantial in-game content than previous Forza Motorsport DLC.
"I'm not going to say any more than it's an expansion pack distinct from the car parks we ship, which we'll absolutely continue to do because we have a brilliant production pipeline that finds awesome cars and gets them into the Forza format," said Fulton.
Expansions will be available as part of the game's previously announced Season Pass.
Announced earlier this year, Forza Horizon is developed by Playground Games, a UK studio created by former DiRT, TOCA and Colin McRae developers, which Forza studio Turn 10 described as a "partner".
It follows the critically-acclaimed racing title Forza Motorsport 4, which was released for Xbox 360 last year.
Forza Horizon will be released for Xbox 360 on October 23.
> Forza Horizon interview: Turn 10 on the festival-inspired racer
Watch the trailer for Forza Horizon below: