This prayer is from the ancient St. Patrick's Lorica, or Corslet. It's common name is "The Breastplate of St. Patrick." The entire prayer is much longer than this. Here is an excerpt and the sung version is even shorter than this:

I rise up today
Thro' a mighty strength
Thro' my invocation of the Trinity,
Thro' my belief in Its threeness,
Thro' my avowal of Its oneness
To the only Creator...
I arise today, (and bind to myself)

God's strenght guiding me,
God's might sustaining me
God's wisdom directing me
God's eye looking before me
God's ear listening to me,
God's word speaking for me,
God's hand protecting me:
The way of God stretching out before me,
The shield of god as my shelter,
The hosts of God guarding me against the snares of the demons,
Against the tempting of my evil desire,
Against the evil inclination of my will
Against everyone who plots against me,
Anear or afar, alone or in a multitude...

Christ with me, Christ before me, Christ after me,
Christ within me, Christ beneath me, Christ above me,
Christ at my right hand, Christ at my left hand,
Christ in my breadth, Christ in my length,
Christ in my height, Christ where I lie,
Christ where I sit, Christ where I arise,
Christ in the heart of every one who thinks of me,
Christ in the mough of every one who speaks of me,
Christ in every eye that sees me,
Christ in every ear that hears me.
Salvation is of the Lord.
Salvation is of the Lord,
Salvation is of the Christ.
May your salvation Lord, be ever with us.

After six years, God spoke to Patrick in a dream and told him to go home. Trusting that God would make a way, Patrick managed to escape and was able to make it all the way home to his family. However, the people from Ireland came to him in his dreams, calling him back.

After becoming a priest and doing great work in Rome, Patrick was made bishop. Because Patrick could speak Celtic and was able to communicate with the Irish, He was eventually sent to Ireland to evangelize. He met with many obstacles. No small one was Druidism, the ancient Celtic religion which was widely practiced in Ireland. They wanted Patrick dead at times. He and his converts were put in prison and sentenced to death, yet he kept to his practice of "spreading God's name everywhere with confidence and without fear." He used a shamrock to explain the Trinity and converted thousands with his gentleness and quiet demeanor. He converted Irish chiefs, set up monasteries, and organized the growing church.

A man more interested in prayer, he turned down gifts from admirers and was known for his humility. He died in 461, having converted practically all of Ireland to Christianity. His feast day is March 17.