The troop increase will bring the total number of U.S. troops in Syria to 500.
A defense official said the additional troops will help train, advise and assist the growing number of Syrian rebel forces preparing to retake and hold Raqqa, ISIS' de facto capital city in Syria.
Carter, who made the announcement at the International Institute for Strategic Studies' Manama Dialogue, said the additional forces will help "to continue organizing, training, equipping, and otherwise enabling capable, motivated, local forces to take the fight to ISIL, and also bringing down to bear the full weight of U.S. forces around the theater of operations like the funnel of a giant tornado."
He added, "This latest commitment of additional forces within Syria is another important step in enabling our partners to deal ISIL a lasting defeat."
The additional 200 troops being deployed to Syria will include special operations forces, trainers, advisers, and explosive ordnance disposal teams.
With support from American airstrikes, as well as advisers on the ground, SDF forces have pushed ISIS out of strongholds in northern and eastern Syria and are now pushing towards Raqqa.
Carter said Saturday that SDF forces have fought their way to 15 miles north of that city.
Plans call for the SDF to envelope Raqqa with Kurdish fighters remaining outside of the city so Arab fighters can retake it from ISIS.
A U.S. defense official said the troop increase "is tied to the growing number of local forces now willing to participate in this fight, and our efforts to enable them."
The SDF has been a mostly Kurdish force with a smaller component of Arab fighters. But as the SDF has grown to 45,000 in number, the number of Arab fighters has also grown to 13,000.
The recruitment of local Arab fighters from the area around Raqqa has helped boost those numbers.
Carter restated during his remarks in Bahrain that after ISIS is defeated in Iraq and Syria, American troops will remain in that country to help with its training and advising mission to help Iraqi forces consolidate security over the rest of the country.