Williams becomes the first to hold the position on the Rams since 2000.
"Mike knows the players in the NFL and the players in our division," said Rams general manager Billy Devaney. "He knows rosters from the bottom up and the top down and how players move on and off rosters in the off-season. He will fill an important role in this area."
Williams joins the Rams after nine seasons with the San Francisco 49ers, the last four as assistant director of pro personnel. He joined the 49ers in 1999 as a volunteer in the personnel department and became a full-time personnel assistant in 2000.
Williams was defensive coordinator at De Anza College in Cupertino, Calif., in 1998 and coached at Southern Utah University (1997). Williams was defensive coordinator at St. Lawrence High School in Santa Clara, Calif., for three seasons.