7 July 1879 is considered as a date or establishment of diplomatic relations between Russia and Bulgaria.
There isn’t a formal document in the historical archives concerning the establishment of diplomatic relations between the two countries after the Russian-Turkish War from 1877-1878 and liberation of Bulgaria from the Osman yoke. But it is known that by the Highest Decree of the Ministry of Foreign Affairs of Russia N 11/25 September 1878, the State Councilor A. P. Davydov “has been appointed Diplomatic Agent and Consul General in Bulgaria (August 18) and has been promoted to Full State Councilor (September 7)”. A. P. Davydov presented his credentials to the Bulgarian Prince A. Batemberg on 25 June/7 July (after the New Style) 1879 and this date was accepted by both countries (by the exchange of notes between the Ministries of Foreign Affairs of Russia and Bulgaria in 1994-1995) as an official date of establishment of diplomatic relations.

In 1886 in the connection with the East Crisis the diplomatic relations between Russia and Bulgaria were broken off and then they were reestablished in 1896.

In 1915, during the First World War, in which Bulgaria took part on Triple Alliance’s side, the diplomatic relations were broken off again.

Established by Brest-Litovsk Peace Treaty (3 March 1918) relations have not been realized in fact. Really, the Head of the Bulgarian Special Mission S. Chaprashikov was in Moscow for some time and he managed to present his credentials to Y. M. Sverdlov. On 13 November 1918 with a decree of VCIC, the Brest Peace Treaty and all incidental agreements were annulled.
The diplomatic relations between the USSR and Bulgaria were established in 1934 on the level of legations (by the exchange of telegrams between the Ministry of Foreign Affairs of Bulgaria and the People’s Commissar of Foreign Affairs of the USSR on 11 and 23 July 1934)
On 5 September 1944, in connection with the fact that during the Second World War Bulgaria was an ally of fascist Germany, the government of the USSR informed the Bulgarian government by a note about the breaking-off of the diplomatic relations and the declaration of war.

The diplomatic relations has been reestablished by the exchange of letters between the Vice-chairman of the Union Control Committee in Bulgaria and the Bulgarian Prime Minister from 14 and 16 August 1945.
On 6 January 1948 was reached an agreement the legations to be transformed into embassies.
On 23 October 1991 in Moscow was signed a Protocol on Establishment of Diplomatic Relations between the Russian Soviet Federative Socialist Republic and Bulgaria. But the arrangements of the Protocol did not make a progress. The countries did not exchange their diplomatic representatives and Russian’s interests in Bulgaria were represented by the Embassy of the USSR.

In December 1991 the Embassy of the USSR was transformed into the Embassy of the Russian Federation.

Russian diplomatic representatives in Bulgaria
1. Alexander Petrovich Davydov – 1879-1880
2. Alexey Mihaylovich Kumani – 1880
3. Mihail Alexandrovich Hitrovo – 1881-1882
4. Alexander Ionin * – 1883-1884
5. Alexander Ivanovich Koyander – 1884-1885
6. Nikolay Kaulbars* – 1886
7. Nikolay Valerievich Charykov – 1896-1897
8. Georgiy Petrovich Bahmetev – 1897-1905
9. Andrey Nikolaevich Sheglov – 1906-1907
10. Dmitry Konstantinovich Kurilo-Sementovskiy – 1907-1911
11. Anatoliy Vasilievic Nekliudov – 1911-1913
12. Alexander Alexandrovich Savinskiy – 1914-1915
13. Feodor Feodorovich Raskolnikov – 1934-1938
14. Anatoliy Iosifovich Lavrentiev – 1939-1940
15. Alexander Andreevich Lavrishev – 1940-1944
16. Stepan Pavlovich Kirsanov – 1945-1948
17. Mihail Feodorovich Bodrov – 1948-1954
18. Yury Kondratievich Prihodov – 1954-1960
19. Georgiy Apollinarievich Denisov – 1960-1963
20. Nikolay Nikolaevich Organov – 1963-1967
21. Alexander Mihaylovich Puzanov – 1967-1972
22. Vladimir Nikolaevich Bazovskiy – 1972-1979
23. Nikita Pavlovich Tolubeev – 1979-1983
24. Leonid Ivanovich Grekov – 1983-1988
25. Victor Vasilievich Sharapov – 1988-1992
26. Alexander Alexeevich Avdeev – 1992-1996
27. Leonid Vladimirovich Kerestedjiants – 1997-2000
28. Vladimir Gennadievich Titov – 2000-2004
29. Anatoliy Victorovich Potapov – 2004

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* Special mission, but he has not been appointed diplomatic agent or consul