Pascal was the son of a respected mathematician and a local administrator in Clermont-Ferrand, France. Early in life Pascal displayed evidence that he was an infant prodigy and apparently discovered Euclid's first 23 theorems for himself at the age of 11. While only 17 he published an essay on mathematics that René Descartes refused to acknowledge as being the work of a youth. Pascal produced (1642–44) a calculating device to aid his father in his local administration; this was in effect the first digital calculator.

Pascal conducted important work in experimental physics, in particular in the study of atmospheric pressure. He tested the theories of Evangelista Torricelli (who discovered the principle of the barometer) by using mercury barometers to measure air pressure in Paris and, with the help of his brother-in-law, on the summit of the Puy de Dôme (1646). He found that the height of the column of mercury did indeed fall with increasing altitude. From these studies Pascal invented the hydraulic press and the syringe and formulated his law that pressure applied to a confined liquid is transmitted through the liquid in all directions regardless of the area to which the pressure is applied. He published his work on vacuums in 1647.

Pascal corresponded with a contemporary mathematician, Pierre de Fermat, and together they founded the mathematical theory of probability. Pascal had been converted to Jansenism in 1646 and religion became increasingly dominant in his life, culminating in the religious revelation he experienced on the night of November 23, 1654. Following this he entered the Jansenist retreat at Port-Royal (1655) and devoted himself to religious studies from then on.