Born in Blackburn, Easterling attended Blackburn High School before graduating with first class honours and distinction in Classics at Newnham College, Cambridge in 1955. After an initial spell lecturing at the University of Manchester (1957-58), Easterling taught within the Cambridge Classics Faculty as a Fellow of Newnham College until 1987 when she took up the position of Professor of Greek at University College London.
In 1994 she returned to Cambridge and Newnham as the 37th Regius Professor of Greek. On retirement in 2001 she became an Honorary Fellow of Newnham College.
In 1998 she was elected a Fellow of the British Academy.