Brosnan was born in Our Lady of Lourdes Hospital in Drogheda, County Louth, Ireland, the only child of Thomas Brosnan, a carpenter, and May (née Smith, born circa 1934). He lived in Navan, County Meath for 12 years and considers it his home town.
He went to Primary School in St. Anne's Primary School, Navan. Brosnan's father abandoned the family when Pierce was an infant. When he was four years old, his mother moved to London to work as a nurse. From that point on, he was largely brought up by his grandparents, Philip and Kathleen Smith. After their deaths, he lived with an aunt and then an uncle, but was subsequently sent to live in a boarding house run by a woman named Eileen.
According to Brosnan,
Childhood was fairly solitary. I grew up in a very small town called Navan in County Meath. I never knew my father. He left when I was an infant and I was left in the care of my mother and my grandparents. To be Catholic in the 1950s, and to be Irish Catholic in the 1950s, and have a marriage which was not there, a father who was not there, consequently, the mother, the wife suffered greatly. My mother was very courageous. She took the bold steps to go away and be a nurse in England. Basically wanting a better life for her and myself. My mother came home once a year, twice a year.
Brosnan was brought up in a Roman Catholic family and educated in a local school run by the de la Salle Brothers while serving as an altar boy.
Brosnan left Ireland on 12 August 1964 and was reunited with his mother and her new husband, William Carmichael, now living in the Scottish village of Longniddry, East Lothian. Carmichael took Brosnan to see a James Bond film for the first time (Goldfinger), at the age of 11. Later moving back to London, Brosnan was educated at Elliott School, a state comprehensive school in Putney, southwest London, now known as Ark Putney Academy. Brosnan has spoken about the transition from Ireland to England and his education in London; "When you go to a very large city, a metropolis like London, as an Irish boy of 10, life suddenly moves pretty fast. From a little school of, say, seven classrooms in Ireland, to this very large comprehensive school, with over 2,000 children. And you're Irish. And they make you feel it; the British have a wonderful way of doing that, and I had a certain deep sense of being an outsider." When he attended school, his nickname was "Irish".
After leaving school at 16, he decided to be a painter and began training in commercial illustration at Saint Martin's School of Art. While attending a rehearsal for a workshop at the Oval House, a fire eater was teaching people how to eat fire and he decided to join. A circus agent saw him busking and hired him for three years. He later trained for three years as an actor at the Drama Centre London. Brosnan has described the feeling of becoming an actor and the impact it had on his life: "When I found acting, or when acting found me, it was a liberation. It was a stepping stone into another life, away from a life that I had, and acting was something I was good at, something which was appreciated. That was a great satisfaction in my life."