Flavius Eusebius (died c. 350) was a Roman military officer and politician. He is usually identified as the father of Eusebia, and consequently as the posthumous father-in-law of the Roman emperor Constantius II.
Biography Born in Thessalonica to a family of Macedonian descent, Eusebius served prior to 347 as the Magister equitum et peditum in the east, probably under the emperor Constantius II.Martindale & Jones, pgs. 307-308 During his time as military commander, he intervened in Armenia, possibly to suppress the revolt of Bacour.Michael H. Dodgeon, Samuel N. C. Lieu, The Roman Eastern Frontier and the Persian Wars (AD 226-363): A Documentary History (1994), pg. 338
After he had retired from this post, he held the rank of Comes and was made consul posterior alongside Vulcacius Rufinus in 347.
Eusebius was probably a Christian.Barnes, T. D., Christians and Pagans under Constantius in L'Eglise et L'Empire au IV Siecle (1989), pg. 317 He had at least three children: his sons Flavius Eusebius and Flavius Hypatius held the consulship together in 359, and his daughter Eusebia married Emperor Constantius II after her father had died.Martindale and Jones, pg. 308
References
Sources Martindale, J. R.; Jones, A. H. M, The Prosopography of the Later Roman Empire, Vol. I AD 260–395, Cambridge University Press (1971)