Was St. Patrick a really Roman Catholic and did he keep the 7th day Sabbath? Does anyone have a  historical reference  that Saint Patrick actually kept the seventh day Sabbath and was not a Roman Catholic?
The life of St. Patrick in a nutshell is that he was the son of well-to-do Roman citizens living in Britannia, captured by Irish raiders, sold into slavery, eventually returned to home after finding his calling, was sent to Rome, became a bishop and was sent back to convert Ireland.  None of this well known history passed down through the ages corroborates that he was 


Not a Latin Catholic (he was born in Britannia, which was a Roman Province ) 



  He had for his parents Calphurnius and Conchessa. The former belonged to a Roman family of high rank and held the office of decurio in Gaul or Britain. 



Didn't give a hoot about Sunday. He certainly cared about Easter Sunday (which in good Catholic tradition considers the Sabbath to start on Saturday night) because that was the day he threw the gauntlet down with the Druids. 



  On Easter Eve, in that year the feast of the Annunciation, and on the summit of the hill kindled the Paschal fire. The druids at once raised their voice. "O King", (they said) "live for ever; this fire, which has been lighted in defiance of the royal edict, will blaze for ever in this land unless it be this very night extinguished." By order of the king and the agency of the druids, repeated attempts were made to extinguish the blessed fire and to punish with death the intruder who had disobeyed the royal command. But the fire was not extinguished and Patrick shielded by the Divine power came unscathed from their snares and assaults. On Easter Day the missionary band having at their head the youth Benignus bearing aloft a copy of the Gospels, and followed by St. Patrick who with mitre and crozier was arrayed in full episcopal attire, proceeded in processional order to Tara. 


You can read all about him in the Old Catholic Encyclopedia this movie about him was pretty good (about par for quality when it comes to saint movies).