The toll of 282,283 includes 81,436 civilians, among them 14,040 children and 9,106 women, said the Syrian Observatory for Human Rights.
Non-jihadist rebel fighters accounted for 48,568 of those killed, while extremist militants -- including non-Syrians -- numbered 47,095.
The Observatory documented the deaths of 101,662 pro-regime fighters, including 56,609 government soldiers.
Another 3,522 of the deaths were unidentified.
Signup to our newsletter and follow us on Facebook and Twitter!
The Observatory is based in Britain and depends on a network of sources inside Syria to gather its information on the conflict that erupted in March 2011.
The toll was the first given since a partial truce came into effect between the government and non-jihadist rebels on February 27.
Several weeks into the truce, the Observatory said violence -- and daily death tolls -- had dropped dramatically.
But since then clashes have broken out in parts of the country where the ceasefire was meant to have taken hold.
The previous toll of 271,138 had been published by the Observatory on February 23.