In 1758, he went with his brother Peter and Matthäus Stach to the missions in Greenland among the Inuit, remaining there four years and helping to found the settlement of Lichtenfels.
[3]After receiving permission from Moravian Church leaders in 1764, Haven travelled to London and met Hugh Palliser, Governor of Newfoundland, and made his intentions to establish a mission known.
His first encounter with Newfoundland Inuit was at Quirpon, and he was able to speak with them in their native tongue, which he had learned while stationed in Greenland.
Because of disagreements between the Moravians and the English authorities over land grants, Haven returned to Europe, spending most of his time in England and the Netherlands.
He went back to England later that year to make arrangements for the proposed mission house, and before returning in 1771, married Mary Butterworth, an English Moravian.