Juozas was one of the five children of the family of Antanas and Ieva Kupraičis. He had a sister, Ona, and three brothers, Petras, Antanas and Jonas.

In 1944, at the request of priest Vytas Baltutis, the Kurpaitis family took in four people of Jewish origin, three of whom were children at the time - Miriam, Iser, Masha and Esther Gail for six months. The Kurpaitis family hid and cared for these people for six months until the area was occupied by the Soviets in October 1944.

At the end of the war, Juozas was sent to work in Germany. After returning to Lithuania he worked on his parents' farm. He was a very kind-hearted person. He was very undemanding to himself, but he was very attentive to others and gave money to everyone who needed it. The war and the occupation disrupted his life. In the post-war years he worked on collective farms. He did not start a family. The last years of his life he lived with his sister's husband's sister Izabela. He died alone in 1984.