Both forms are correct. Both fulfill and fulfil are accepted forms in English language. Fulfill is widely use as an American spelling, while fulfil is correct in British English (hence it is mostly used in UK, Australia and other English speaking countries of British origin). American spelling, fulfill, was accepted due to Noah Webster dictionary, which simplified most spellings (as you may notice, this form is longer so it doesn’t look simpler, however it is probably connected to the spelling of word fill, so the form fulfill did in fact make it simpler for users).

Correct spelling

fulfill

Correct spelling, explanation: most popular spelling in American English, correct also in Canada.

Correct spelling

fulfil

Correct spelling, explanation: most popular spelling outside North America, correct also in Canada.

Definition of fulfill/fulfil:
verb, to carry out; to meet expectations, reach the goals etc.
To get the mortgage you have to fulfill the conditions.
You do not fulfil your duties, Mark. You have to try more.


Incorrect spelling

fullfil

Incorrect spelling

Incorrect spelling

fullfill

Incorrect spelling

Incorrect spelling

fufill

Incorrect spelling