in 1815 he was appointed adjutant general for the swedish army and in 1820 to lieutenant general. björnstjerna was from 1828 to 1846 the swedish minister resident in london. in 1815 he was created baron () stånd, count in 1826, he was appointed the royal order of the seraphim in 1838 and in 1841 the lord of the realm. in 1843 he was appointed marshal.