Jules Cardinal Mazarin was born Guilio Mazarini on July 14, 1602 either in Rome or Piscina in the Abruzzi to a very old and prominent Sicilian family. His father served as majordomo to the powerful Colonna family in Rome, and his uncle, also named Guilio Mazarini (1544-1622), was a famous Jesuit priest in Bologna famous for his sermons and sacred writings. He began his education with the Jesuits in Rome, and in 1619 he started studying law at the University of Alcalá under Jerome Colonna, and when he returned to Rome in 1622 he became a captain of pontifical troops under the Colonnas. Note that he was never actually ordained a priest and only held minor orders.
Mazarin had a very lively youth. In 1622 (at the age of 20!), as previously noted he was a captain of pontifical troops under the Colonnas. Gradually, his focus began to shift from the military to the diplomatic sphere, and by 1626, he became a papal diplomat, serving in the in the Valtelline War, and later again in the Mantuan War of Succession (1628-1630). The truce he negotiated in 1630 between the French and the Spaniards and the Duke of Savoy so pleased Cardinal Richelieu and was the beginning of their association. The Spaniards tried to ruin his name with Pope Urban VIII, but the influence of Cardinal Barberini and Richelieu thwarted that, and he was made canon of the Lateran, vice-legate at Avignon (1632) and the nuncio extraordinary to France (1634). However, the Spanish complained to Rome that as Papal Nuncio to France that it seemed Mazarin was far too pro-French in his policies, so Urban had him dismissed in 1636. Soon after leaving papal service, Richelieu took him in his service and he was naturalized a French citizen in 1639. In 1641, Mazarin was made cardinal, and a year later, Richelieu, on his deathbed, recommended him as his successor to the Prime Ministership of France. After Richelieu's death in 1642, Louis XIII, who was also not in particularly good health, announced the Council of Regency, and Mazarin was named its head, while his wife Anne of Austria held nominal power. In 1643, on Louis XIII's death, Anne of Austria, as Queen Regent, named Mazarin Prime Minister of France.
Anne of Austria seemed to have a great deal of affection for Mazarin, and the precise nature of their relationship is hotly contested by historians. There have been rumors since the time that the two were lovers, perhaps even secretly married, and that Louis XIV was actually their son. These rumors were fueled by the fact that an autopsy performed on Louis XIII after his death showed him to be sterile. Whatever the character of their relationship, they were extremely close, and that guaranteed his position of power.
As Prime Minister of France with Anne of Austria as Queen Regent, he continued much of Richelieu's policies, especially his policies against the House of Austria. In 1648 he was able to negotiate favorable terms for France in the Peace of Westphalia that ended the Thirty Years' War, taking for France the region of Alsace, but without Strasbourg. In 1659 he again negotiated favorable terms for France in the Peace of the Pyrenees that ended the war with Spain, and France received Roussillon, Cerdagne, and part of the Low Countries in the deal. His foreign policy, was on the whole, indifferent to the interests of Catholicism, just as Richelieu's had been. The Peace of Westphalia legally recognized the existence of Calvinism in Germany, and Mazarin rewarded Protestant princes with secularized bishoprics in exchange for their opposition to Austria.
The Fronde insurrection was mainly directed against Mazarin and attempted to limit his power and that of the Crown, and was fueled by the personal ambitions of discontented nobles and by financial burdens imposed on the people by his policies. In 1648 the Parlement rejected a fund raising scheme proposed by Anne of Austria and Cardinal Mazarin, which would have involved cutting salaries for most of the high courts, and drafted a reform document limiting the royal prerogratives for them to do that. In retaliation, Mazarin had several members of Parlement arrested, most notably Pierre Broussel, but the Parisian populace rose in revolt and barricaded the streets. Mazarin was forced to acquiesce and had them released. The Peace of Westphalia which was negotiated later that year, on the other hand, freed the army to take action against the Frondeurs. Anne and Mazarin left Paris secretly in 1649, while the Royal army under the command of Louis II de Bourbon, prince de Condé blockaded the city. A comporomise negotiation was made later that year.
Louis de Bourbon, after having aided Anne and Mazarin now expected to control them. His overbearing attitude and intriguing had him arrested in 1650, and this precipitated a second Fronde. His sister, Madame de Longueville, called upon Marshal Henri de Turenne for aid in releasing her brother, and though his troops and Spanish allies were ultimately defeated, many other nobles joined in support, and Mazarin was forced to yield. Mazarin then fled France for Germany in 1651, but the victorious nobles then began to quarrel amongst themselves. Around this time Louis XIV reached majority, and that further divided the nobles. As the Fronde began to disintegrate, Mazarin returned to France, and resumed power. This ultimate defeat of both Frondes humiliated the nobles, and paved the way for royal absolutism, the foundation of Louis XIV's future omnipotence.
In 1653 Louis XIV attained majority and the Council of Regency was dissolved, but Louis retained Mazarin as Prime Minister, and he continued to centralize government power in the hands of the Crown. He died on March 9, 1661 at Vincennes, with Louis XIV prepared to take absolute power.
Catholic Encyclopedia, Jules Mazarin, http://www.newadvent.org/cathen/10092a.htm