Roman senator, d. about 409. In youth he frequented the schools of rehetoric with St. Jerome. In 385 he married Paulina, second daughter of St. Paula. He was probably among the viri genere optimi religione præclari, who in 390 denounced Jovinian to Pope St. Siricius (Ambrose, Ep. xli). When he attacked St. Jerorme's book against Jovinian for prudential reasons, Jerome wrote him two letters (Epp. xlviii-ix, ed. Vallarsi) thanking him; the first, vindicating the book, was probably intended for publication. On Paulina's death in 397, Pammachius became a monk, that is, put on a religious habit and gave himself up to works of charity (Jerome, Ep. lxvi; Paulinus of Nola, Ep. xiii). In 399 Pammachius and Oceanus wrote to St. Jerome asking him to translate Origen's "De Principiis", and repudiate the insinuation of Rufinus that St. Jerome was of one mind with himself with regard to Origen. St. Jerome replied the following year (Epp. lxxxiii-iv). In 401 Pammachius was thanked by St. Augustine (Ep. lviii) for a letter he wrote to the people of Numidia, where he owned property, exhorting them to abandon the Donatist schism. Many of St. Jerome's commentaries on Scripture were dedicated to Pammachius. After his wife's death Pammachius built in conjunction with St. Fabiola (Jerome, Epp. lxvi, lxxvii), a hospice at Porto, at the mouth of the Tiber, for poor strangers. The site has been excavated, and the excavations have disclosed the plan and the arrangement of this only building of its kind. Rooms and halls for the sick and poor were grouped around it (Frothingham, "The Monuments of Christian Rome," p. 49). The church of SS. John and Paul was founded either by Pammachius or his father. It was anciently known first as the Titulus Bizantis, and then as the Titulus Pammachii. The feast of Pammachius is kept on 30 August.
(Taken from Catholic Encyclopedia)