The Uefa club financial control adjudicatory chamber ordered the ban after Galatasaray "failed to comply with the terms of the settlement agreement" made with the European body in May 2014, said a statement.
Galatasaray have spent heavily in recent years to buy the likes of Germany's World Cup winner Lukas Podolski and Dutch star Wesley Sneijder. They have also been ordered to cut back on wages.
But Uefa referred the case to its tribunal in January after Galatasaray did not balance its budget for the 2015-2016 season as promised.
Uefa said Galatasary would be banned from European competition for the next season it qualifies in 2016-2017 and 2017-2018 seasons.
"The Turkish club has also been ordered to limit the overall aggregate cost of employee benefits expenses of all of its players in each of the next two reporting periods" for 2016 and 2017, Uefa said.
Galatasaray, who failed to get beyond the Champions League first round group this season and went out of the Europa League to Roma last week, said it hoped to be back in European competition after one year.
The team are having a poor Turkish Super Lig campaign and are currently in fifth place, outside even a chance to play in the Europa League next year.
Coach Mustafa Denizli resigned on Tuesday after just three months in the job.
"We will have to evaluate this very carefully," Galatasaray general secretary Fatih Isbecer told the DHA news agency after the decision was announced.
"We need to pay our penalty after winning the right this year to compete in Europe.
"We will continue to save money with our revised rationalisation plan. And in a year's time we will again get ready our plan to be in the Champions League (for 2017/18). There is no need to be too pessimistic."
Uefa implemented its financial fair play rules in 2011 in a bid to force clubs to balance their books. Every club in European competition is assessed and bans are the toughest sanction. – AFP