The Liga club were handed the sanction in April after irregularities were found in their dealings at youth level.
FIFA suspended the punishment pending an initial appeal to the governing body, which was dismissed, with the Catalan club subsequently opting to the take the case to CAS.
Uruguay striker Luis Suarez has been among those to join Barca while the embargo has been on hold, making the switch from Liverpool for a fee in the region of €80 million.
However, Barca will now be unable to add to their squad until 2016 after CAS determined FIFA's original decision to ban them from making signings for two transfer windows should stand.
In a statement, Barca expressed "its total disagreement with the resolution" and revealed their intention to explore their legal options, once the reasons for the dismissal of the appeal have been published.
"FC Barcelona wants to state its total disagreement with the decision of CAS reported on Tuesday which confirms the sanctions imposed by FIFA as a result of alleged violation of the rules on international transfers of players under age," the statement read.
"The club has made it clear to the FIFA Disciplinary Committee, the FIFA Appeals Committee and to CAS, that it shares and supports the policy of protection of minors and concern for their development and training.
"This is confirmed by the conduct of the club throughout its history, and it has become a world example in terms of schooling and teaching of young players and the formative work carried out. The structure of the FC Barcelona training setup has enabled hundreds of young players to fulfil their dreams and train as people.
"Errors that the club may have made, and which have been recognised and argued by the relevant authorities are, in any event, administrative and caused largely by the existing regulatory conflict between the regulations of FIFA and the Spanish legislation. The conviction of the club was that it acted correctly.
"Therefore, FC Barcelona considered the sanction completely disproportionate, as it represents far too heavy a punishment for the club when taking into account our background and the circumstances in this particular case.
"In this sense, when the club is notified of the legal basis for CAS' decision, we shall study and assess the various legal options available, including the possibility of challenging the CAS decision at the Swiss Federal Tribunal."
