One former guard was found guilty of murder with three others guilty of voluntary manslaughter.
A further 17 Iraqis were injured as the private contractors opened fire to clear the way for a US convoy.
The shootings sparked international outrage and a debate over the role of defence contractors in warfare.
Prosecutors said the Blackwater guards had harboured deep hostility toward Iraqis and boasted of  firing their weapons indiscriminately.
Nicholas Slatten was found guilty of murder while Paul Slough, Evan Liberty and Dustin Heard were found guilty of at least three charges of voluntary manslaughter and also face gun charges.
A US federal jury has found four Blackwater security guards guilty of killing 14 Iraqis in a square in Baghdad in 2007.