Documented: the English faculty page for Charles M. Lieber at Tsinghua Shenzhen International Graduate School (SIGS) states that after Columbia (1987–1991) he held a faculty position at Harvard University (1991–2023), served as Chair of the Department of Chemistry and Chemical Biology (2015–2020), and was named a University Professor (2017). A later SIGS news item calls that 2017 appointment the Joshua and Beth Friedman University Professor, which it describes as Harvard’s highest faculty distinction.
The January 2020 FBI affidavit in support of the criminal complaint states he was a full-time faculty member and Chair of that department and had been affiliated with Harvard since approximately 1991.
The Harvard Crimson later reported a university spokesperson confirmed he retired from Harvard on February 1, 2023. See that post.