After having pursued studies in history at the Faculty of Arts of Charles University in Prague, he joined the Military Historical Institute in 1956.
He was one of the founders of the Committee for the Defense of the Unjustly Prosecuted (VONS), a signatory of Charter 77, and promoter of the meetings between Czech and Polish dissidents in the Giant Mountains.
In 1980, he left Czechoslovakia and initially went to Germany, only to later settle in France where he continued his political activities.
[1] As a historian well trained in archival work, Tesař has left two important collections that concern the history of the Czechoslovak dissident movement.
One of them is currently located at the Museum of Moravia, while the other is held in the collections of La contemporaine in France.