The endorsement from Clyburn comes as Clinton battles with Vermont Sen. Bernie Sanders for support among minority voters before the Nevada Democratic caucuses Saturday and South Carolina's presidential primary Feb. 27.
Clyburn, the House assistant Democratic leader who’s among the most influential Democrats in his state, remained neutral in the 2008 presidential primary, and was expected to do the same this year until close friend and family urged him to make an endorsement.
The South Carolina Democrat's office did not return a request for comment on the endorsement.
He is expected to endorse Clinton at 11 a.m. Friday at Allen University in Columbia. Clinton will not be in attendance at the event.