Joshua Gosselin joined the Guernsey Militia in 1758 and over a military career of forty years rose to the rank of Colonel in 1789. He was elected a Greffier of the Royal Court in 1768. Gosselin had a deep love of nature and made a comprehensive list of the wildflowers of Guernsey, the earliest record of its kind. He also collected and studied seashells, was a noted antiquarian and an important figure in Guernsey society.