 He was a commissary in Brussels for negotiating a commercial agreement with Austria and the Netherlands from 1752 to 1755 and an envoy to Prussia from 1756 to June 1765 and from December 1765 to his death.In May 1756, Mitchell arrived in Berlin, and was enthusiastically received by Frederick.Prior to this, antagonism had steadily been building between France and England over shipping and territory rights, and the British king, concerned with the exposure of his Hanoverian territories should war arise, wished to draw closer to Prussia.