Troopers say the crash happened in the shoulder of the westbound lanes of I-90 near exit 54 on the Kittitas County side of Snoqualmie Pass.
A tow truck was helping a driver that had become stuck in the snow on the freeway's right shoulder around 5 p.m. Meanwhile, a third car driving in the left lane lost control and slid across the freeway, striking the back of the disabled vehicle and then crashing into the tow truck driver, killing him.
The victim has been identified as 46-year-old Jason Halstead of North Bend. No one else was hurt.
Troopers say they are still investigating whether any charges will be filed.
Several other collisions forced state transportation officials to close I-90 through the pass for much of Sunday evening. The pass reopened Monday morning with chains required as heavy snow and near whiteout conditions persisted.