He was a lecturer at a number of Irish third-level institutions, and then professor at, and later president (2012–2016) of, Ireland's main teacher training college, St Patrick's, Drumcondra.

His father owned and ran Peter's Pub between South William Street and St Stephen's Green in central Dublin.

[6] He then studied for the priesthood at the Pontifical Gregorian University in Rome, and while he did not pursue ordination,[4] received a qualification (BPh) there.

[17] Keogh's research and publications work addresses aspects of Irish history including politics, education, religion and gender.

[8][19] Keogh became a member of the Policy and Standards Committee of Quality and Qualifications Ireland, the state body responsible for overseeing the Irish third-level qualifications framework and quality assurance structures, in April 2017,[20] and resigned with effect from July 2020, after his appointment as DCU president.

[28] Keogh was selected in December 2019, after an 18-month international search process,[29][6] and appointed by the Governing Authority for a term of ten years.

[8] Keogh has authored or edited, individually or jointly, at least 16 books[30] on aspects of history, and various papers, as well as contributing multiple articles to the Dictionary of Irish Biography.

[31] Books: Articles: In November 2000 Keogh married Katherine (Katie) Schott, from Indianapolis, Indiana, at the on-campus basilica of the University of Notre Dame.

[47] His wife, a graduate of Notre Dame (Lewis Hall, 1998),[48] later a project manager and communications specialist,[8] had moved to Ireland as associate director of the Dublin branch operation of the university in 1998.