Clark was found guilty Tuesday on six charges and faces up to 18 years in prison when he is sentenced at a later date.
Clark was also convicted of a so-called gang aggravator due to his involvement with Seattle's West Side Mobb and could receive up to five years of additional time.
The Seattle Times said Clark's lawyer, Alfoster Garrett, unsuccessfully argued that his defendant's case was not what the Washington Legislature had in mind when it passed the human-trafficking statute in 2003.
"This is the first time it's been applied in the state," Garrett said. "The Legislature didn't intend human trafficking to be used this way."