A native of St. Florian, Austria, Gruber entered the Society of Jesus in Vienna in 1641 and was ordained a priest in Graz in May 1655. In response to his request to be sent to the China mission, the superior general called him to Rome and instructed him to travel via the Middle East and the Silk Route to China. Not finding this possible, he followed the southern sea route via Surat, India, and Macao.
In July 1658, ten months after his arrival in Macao, he received orders to go to Peking (Beijing) and proceed along a northern route to Europe. Again finding this impossible, Gruber left Peking in 1661 and went to Sian (Xi'an) to meet Albert Dorville, and together they traveled via the western region of Sinkiang (Xinjiang), Tibet, and Nepal to Agra, India, where Dorville died. Gruber reached Hormuz by sea, went overland through the Middle East, and proceeded to Rome.
Still intent on entering China via a northern land route, he traveled to Riga, Latvia, where he learned that the Russians would not issue him a transit visa. Traveling to Constantinople, he fell ill and returned to Italy. He became a military chaplain for two years and was a pastor at Tyrnau (or Trnava, in present day Slovenia) and at Trencn until his death at Sarospatak, Hungary.