Berner began his diplomatic career in 1960 and held various positions, including serving at the Swedish UN delegation, SIPRI, and embassies in Beijing and Moscow.

After retirement, he remained active in international relations, serving on boards and advising organizations focused on Swedish-Russian cooperation.

He then held the same position at the Swedish embassy in Moscow from 1971 to 1974 before becoming a desk officer (departementssekreterare) at the political department of the Ministry for Foreign Affairs in 1976.

[1] During his posting in Moscow, he was also accredited to Mongolia (1989–1992),[6] Armenia (1992–1994), Azerbaijan (1992–1994), Georgia (1992–1994), Belarus (1992–1994), Kazakhstan (1993–1994), Kyrgyzstan (1993–1994), Tajikistan (1993–1994), Turkmenistan (1993–1994), and Uzbekistan (1993–1994).

[12] Berner later remarried Benedicte Eyde (born 1955), the daughter of Sigurd Mörner-Eyde and Kate (née Schröder).