Henry III developed a military and political career during the French Wars of Religion before becoming king. As duke of Anjou he commanded royal forces against the Huguenots and later directed the siege of La Rochelle. Elected king of Poland in 1573, he spent only a short period there. The death of his brother Charles IX in 1574 brought him back to claim the French crown, and he was crowned at Reims in 1575.

His reign required repeated negotiation between armed religious groups, powerful nobles and a monarchy short of money. Peace settlements granting concessions to Protestants provoked militant Catholic opposition, while renewed restrictions failed to secure a lasting settlement. His mother, Catherine de Medici, remained an adviser and negotiator. Henry also developed elaborate court ceremonial and promoted trusted favourites, seeking to reinforce royal authority.

The succession made the conflict more dangerous. After his younger brother died in 1584, the Protestant Henry of Navarre became the heir under the customary rules of inheritance. The Catholic League, led by the Guise family and supported by Spain, resisted that prospect. Pressed into further anti-Protestant measures, Henry III found himself losing freedom of action to a movement that claimed to defend the faith more effectively than its king.

During the Day of the Barricades in 1588 he lost control of Paris and withdrew. Later that year he ordered the killing of the duke of Guise and the duke's brother at Blois. The action removed rivals but intensified rebellion and religious hostility toward him. He then allied with Henry of Navarre and prepared a campaign against Paris. In August 1589 the Dominican friar Jacques Clement stabbed him, and he died from the wound. The last Valois king left a disputed succession rather than a religious settlement. His career shows a monarch attempting to preserve royal authority amid civil war, whose tactics repeatedly weakened the alliances he needed.