Millett was the assistant curator of archaeology at the Hampshire County Museums from 1980 to 1981. He then began his academic career, and joined Durham University in 1981. He was a lecturer from 1981 to 1991, and senior lecturer from 1991 to 1995. He was Professor of Archaeology between 1995 and 1998.[1]
Millett excavated a Roman-period site in Yorkshire (with Peter Halkon). He is the director of the Roman Towns Project (with Simon Keay and the British School at Rome), and also the director of the Greek Colonization and Archaeology of European Development project. Millett has profoundly changed Romano-British archaeology by implementing and calling for new approaches to the excavated materials.
Outside his university work Millett holds a number of appointments. He is a vice-president of the British Academy with responsibility for the British Academy Sponsored Institutes and Societies.[2] He has held three senior positions at the Society of Antiquaries of London: he was director from 2001 to 2007, treasurer from 2007 to 2011,[1] and its president since 2021.[7] He is a member of the Antiquity Trust, which supports the publication of the archaeology journal Antiquity.[8]
1980: The Roman Riverside Wall and Monumental Arch in London - Excavations at Baynard's Castle, Upper Thames Street, London, 1974-76. (With Charles Hill and T. F. C. Blagg. London: London and Middlesex Archaeological Society). ISBN9780903290180.
1986: Excavations on the Romano-British Small Town at Neatham, Hampshire, 1969-1979. (Withh David Graham. Southampton: Hampshire Field Club). ISBN9780907473015.
1995 (edited with J. Metzler, N. Roymans and J. Slofstra) Integration in the Early Roman West: the role of culture and ideology (Dossiers d'Archéologie du Musée National d'Histoire et d'Art IV (IVth Archaeological Papers of the National Museum of History and Art, Luxembourg). ISBN9782879640334.
Shiptonthorpe, East Yorkshire: archaeological studies of a Romano-British roadside settlement (Yorkshire Archaeological Society Roman Antiquities Section monograph). doi:10.1080/00665983.2007.11020726.
2005 (with S. Keay, L. Paroli, and K. Strutt) Portus: An Archaeological Survey of the Port of Imperial Rome (British School at Rome Monograph) Right. ISBN9780904152470.
2013: Ocriculum (Otricoli, Umbria) - An Archaeological Survey of the Roman Town. (With Sophie Hay and SJ Keay. The British School at Rome). ISBN9780904152678.
2015: Hayton, East Yorkshire - Archaeological Studies of the Iron Age and Roman Landscapes. Volume 1 (With P. Halkon and Helen Woodhouse. Yorkshire Archaeological Society, Roman Antiquities Section). ISBN9780993238321.