CAS said Fifa's sanctions against Suarez are '"generally proportionate to the offence committed.''
Suarez can next play for Barcelona on Oct 26, which could be the day the team faces Real Madrid in the Spanish league. He remains banned for Uruguay's next eight competitive matches and will miss next year's Copa America and some World Cup qualifying matches.
Suarez bit Italy defender Giorgio Chiellini's shoulder during Uruguay's 1-0 win at the World Cup on June 24. He denied it at first, but later admitted it and apologised within days.
"The sanctions imposed on the player by Fifa have been generally confirmed,'' the court said in a statement.
The court described the ban imposed by Fifa on Suarez from taking part in any football activity as "excessive.''
"However, the 4-month suspension will apply to official matches only and no longer to other football-related activities (such as training, promotional activities and administrative matters),'' the court said.
Banning Suarez from training would have meant the ban "would still have an impact on his activity after the end of the suspension,'' the panel ruled.
Suarez, who left Liverpool for Barcelona after the World Cup, appeared at the court's fast-track hearing last Friday in an effort to reduce his ban.
Fifa had also fined him 100,000 Swiss francs ($112,000).
CAS will publish its reasons for the verdict in the coming weeks.
Suarez, who was supported in his appeal by Barcelona and the Uruguay football federation, could challenge the ruling at the Swiss Federal Tribunal. That is a much longer process, and the court only intervenes if legal process was abused.
Suarez is also set to miss three of Barcelona's six Champions League group matches.
After being sent home from the World Cup before Uruguay's second-round loss to Colombia, Suarez has eight matches of his competitive internationals ban still to serve. He would be allowed to play in non-competition friendly matches.
Suarez has bitten opponents on other occasions as well, when playing for Ajax in 2010 and Liverpool last year.
"I deeply regret what occurred,'' Suarez wrote in a Twitter message shortly after his ban at the World Cup was announced. "(The) truth is that my colleague Giorgio Chiellini suffered the physical result of a bite in the collision he suffered with me.''