France automatically qualified for 2002 World Cup
Fifa president Sepp Blatter announced the major change in policy following a meeting of the organisation's executive committee on Friday.
The board decided the defending champions should no longer get automatic entry for the subsequent World Cup.
"It's something that's been thought about for some time," Fifa General Secretary Michel Zen Ruffinen told BBC Sport Online.
"We feel it's not proper that the winners shouldn't play in competitive matches before having to defend their championship.
"Two years of friendlies often means they aren't as ready as their rivals when the tournament starts."
Defending champions France will be the last winners to gain a free ticket to the next finals.
Fifa's decision breaks a tradition that has stood since the first World Cup in 1930.
The only time the champions have not defended their title was in 1934 when 1930 world champions Uruguay chose not to enter the competition in Italy.
"We've taken quite an historic decision," said Blatter.
"The champion of Korea and Japan 2002 will not be automatically qualified. This is new and even brand new."
Blatter said it was to allow the champions the chance to have official matches in the build-up to the following tournament.
In recent years, automatic qualification has been regarded as less of an advantage.
The defending champions have played meaningless friendlies, while their rivals have maintained their competitive sharpness in qualifying matches.
The decision creates an extra slot in the 32-nation finals and brings the World Cup in line with regional championships.
Winners of the European and South American championships do not automatically qualify for the next finals.
Zen Ruffinen would not commit Fifa to where that other spot would go but did admit that a solution was needed for Oceania.
"Weżve had a lot of suggestions that they should have a direct place but we have to consider if their representatives would be able to do themselves justice in the Finals.
"When I go to Sydney I emphasise personally that I would like to give them a permanent slot but Fifa as a whole has the final say.ż
The General Secretary also dismissed the notion that Oceania is over-looked because it's football market isnżt as prosperous as elsewhere in the world.
"We are very helpful to this region - we allow a New Zealand team to play in the Australian League to help both countries and I think Soccer Australia are well aware of what we do for them."
The introduction of Fifa's unified calendar next year would also cause problems for automatically qualified world champions.
With dates of competitive and friendly games to be standardised on a worldwide basis it would be harder for the champions to arrange friendlies.
The new calendar will also spell the end for the current South American qualifying format, which involves all teams playing 18 games each in a league.
"It will no longer be possible for the South Americans to run their qualifying competition like that and a new format will have to be found," said Blatter.
There will be live coverage from 1000 GMT on BBC Two, BBC Sport Online and BBC Radio Five Live.