Westling joined the Boston University faculty in 1974. He was named provost in 1984. In this role he was controversial B.U. president John Silber's top aide and twice severed as acting president; first in 1987 while Silber was on sabbatical and again in 1990 while Silber was running for Governor. In 1996, he was chosen to succeed Silber, who became Chancellor of the University after a 25-year tenure as president. Westling's tenure came to an end in July 2002, when he resigned the presidency to return to teaching and research as a Professor of History and Humanities. Silber stepped down as chancellor and reassumed the presidency on an interim basis until Aram Chobanian was appointed president ad interim in October 2003.