Barcelona will serve a transfer ban beginning in January 2015 after Fifa rejected appeals lodged by the club and the Spanish football federation.
The Spanish giants were handed a 14-month ban in April after being judged to have breached rules on signing international players under the age of 18.
An appeal allowed the club to conduct transfer business this summer but Fifa's ruling will now prevent them from participating in next year's January transfer window and the following summer transfer window.
A statement from world football's governing body read: The Fifa Appeal Committee has decided to reject the appeals lodged by Spanish club FC Barcelona and the Real Federación Española de Fútbol (RFEF) and to confirm in their entirety the decisions rendered by the Fifa Disciplinary Committee in the respective cases relating to the protection of minors.
"As such, FC Barcelona is to serve a transfer ban which will see the club prevented from registering any players at both national and international level for two complete and consecutive transfer periods, starting with the next registration period (January 2015) given that the appeal of the club had been granted suspensive effect by the chairman of the Fifa Appeal Committee.
"FC Barcelona has also been ordered to pay a fine of CHF 450,000 and been given a period of 90 days from today in which to regularise the situation of all minor players concerned."
After Fifa's decision was delayed by appeals lodged by the club, Barcelona embarked on a transfer spree that has seen them spend in excess of £130m.
The club have strengthened all areas of their team following a trophy-less campaign last term, adding Luis Suarez, Thomas Vermaelen, Jeremy Mathieu, Ivan Rakitic, Marc-Andre ter Stegen and Claudio Bravo to their ranks.
The club have 11 days remaining of the current transfer window to make further additions before they are banned from transfer activity until January 2016.