The family belonged to the Reformed Church, a fact that made Lenaert and his younger brother Dirck Jansz Graeff work in a social-political direction.

In 1564, Lenaert was a member of a delegation who spoke with the Spanish Regent Margaret of Parma about the political situation in Amsterdam and the province of Holland.

[3] In March of that year, backed by De Graeff, his brother Dirck Jansz and a large part of the bourgeoisie, Henry, Count of Bréderode became the General-captain of the city.

[1] Lenaert Jansz de Graeff became his friend, adviser, and vice-general-captain of Amsterdam, at the head of a newly formed company of 400 citizens.

In August — on the arrival of Fernando Álvarez de Toledo, 3rd Duke of Alba — he left the city with his second wife, Griet Hendriksdr Rooclaas, because he was suspected of Calvinist leanings.

[3][4] In March they cruises in the North Sea, and on April 1, 26 ships, including De Graeff's, managed to get into the Meuse estuary off Brielle through a heavy Storm.