In 1573 he married Anne Gueniot and had one daughter, Charlotte Jeannin.

A pupil of the great jurist Jacques Cujas at Bourges, he was an advocate at Dijon by 1569 and became councillor and then president of the parlement of Burgundy.

As councillor to Charles of Lorraine, Duke of Mayenne, he sought to reconcile him with King Henry IV of France.

After the victory of Fontaine-Française (1595), Henry took Jeannin into his council and in 1602 named him intendant of finances.

He took part in the principal events of the reign, negotiated the Treaty of Lyon with Charles Emmanuel I, Duke of Savoy, and the defensive alliance between France and the United Netherlands in 1608.