It is located approximately 50 kilometres (31 mi) north of the Polish capital Warsaw, on the Warsaw-Gdańsk rail line and serves as a railway junction.

In the past, the name of the town was spelled in different forms: Nasilzco, Nosidlsk, Nosylsk, Nosydlsk, Nosielsk, Nosselia, Nosidlsko, Nasidlsko, Nosilsko, Nasilsko, Nasylsco.

On November 11, 1386, Janusz I of Warsaw granted the remaining part of the town of Nasielsk (civitas Nostra Nosielsko) to the knight Jakusz of Radzanow (Prawdzic coat of arms).

During the Polish-Soviet War, in August 1920, Polish forces won the Battle of Nasielsk against the advancing Red Army.

Following the joint German-Soviet invasion of Poland, which started World War II in September 1939, the town was occupied by Germany until 1945, and the population was subjected to repressions.

[2] In April 1940, the Germans arrested the pre-war Polish mayor Feliks Rostkowski, and imprisoned him in a concentration camp; however, he survived and returned to Nasielsk after the war.

[3] Expelled Poles were held in a camp in Działdowo for two weeks, where they were stripped of valuables, and then deported in freight trains to the Radom District of the General Government, while their houses and workshops were handed over to German colonists as part of the Lebensraum policy.

The officially protected traditional food produced in Nasielsk is local cold pressed linseed oil (as designated by the Ministry of Agriculture and Rural Development of Poland).