An ambitious and self-esteeming person, he followed a policy of expansion for his duchy. In the autumn of 1588, taking advantage of the civil war weakening France during the reign of his first cousin Henry III, he occupied the Marquisate of Saluzzo, which was under French protection. The new king, Henry IV, demanded the restitution of that land, but Charles Emmanuel refused, and a war ensued. The broader conflict involving France and Spain ended with the Peace of Vervins (May 2 1598), which left the current but separate question of Saluzzo unsolved. After the Duke had started talks with Spain, Henry threatened to reopen the war, until, with the Peace of Lyon (January 17 1601) Saluzzo went to Savoy in exchange for Bresse and other territories over the Alps. By terms of the treaty the eradication of Protestants was to be carried on in the Duchy.
With the Treaty of Bruzolo (April 25 1610) Charles Emmanuel allied with France against Spain, but the assassination of Henry IV changed the situation, as the treaty was not recognized by Marie de' Medici, who immediately assumed regency for Henry's son Louis XIII, a minor. Nevertheless, Charles Emmanuel obtained the help of French troops to free Alba from the Spaniards (January 1617), as the new King Louis XIII resumed his father's former alliance with Savoy. His sister Christine Marie was married with Charles Emmanuel's son, Victor Amadeus in 1619.
However, when the French occupied Casale Monferrato during the War of the Mantuan Succession, Charles Emmanuel allied with Spain. When Richelieu invaded Piedmont and conquered Susa, the duke changed sides again and returned to an alliance with France. However, when Philip IV of Spain sent two invasion forces from Genoa and Como, Charles Emmanuel declared himself neutral, and in 1630 Richelieu ordered a French army to march into Savoy to force him to obey the pacts. The French troops, soon backed by another army, occupied Pinerolo and Avigliana. The Savoy army under Victor Amadeus was defeated in Lower Valsusa.
The duke, caught by a violent fever, died suddenly at Savigliano in late July 1630. He was succeeded by his son Victor Amadeus.
| Charles Emmanuel I, Duke of Savoy | Father: Emmanuel Philibert, Duke of Savoy | Paternal Grandfather: Charles III, Duke of Savoy | Paternal Great-Grandfather: Philip II, Duke of Savoy |
| Paternal Great-grandmother: Claudine de Brosse | |||
| Paternal Grandmother: Infanta Beatriz, Duchess of Savoy | Paternal Great-Grandfather: Manuel I of Portugal | ||
| Paternal Great-Grandmother: Maria of Aragon | |||
| Mother: Margaret of France, Duchess of Berry | Maternal Grandfather: Francis I of France | Maternal Great-Grandfather: Charles, Count of Angoulême | |
| Maternal Great-Grandmother: Louise of Savoy | |||
| Maternal Grandmother: Claude of France | Maternal Great-grandfather: Louis XII of France | ||
| Maternal Great-Grandmother: Anne of Brittany |
He married his cousin Catherina Micaela, daughter of Philip II of Spain and Elizabeth of Valois and had ten children:
After the death of his wife, he never remarried but was father to another eleven illegitimate children from 1600 onwards by the following mistresses, Luisa de Duing, Argentina Provana, Marguerite de Roussilon, Virginia Pallavicino, Anna Caterina Meraviglia and Anna Felizita Cusa.