The first attempt to found an Association of Reserve Officers made major (r) Dimitar Popov in 1903, followed by colonel Kiril Kozlovski and the brothers colonels Mikhail and Ivan Popov in 1906. In the summer of 1907 in Sofia was established a reservists club as a professional society. On 

Sep.16, 1907 a number of reserve officers met and decided to found the first reserve officers organization in Sofia and also made an appeal for building such units in the countryside. Then a statute of the organization has been adopted and a leadership chaired by Maj. Gen. (r)  Nikola Bochev has been elected. Two weeks later, on September 30 the leadership took a decision to establish the Union of Reserve Officers (URO) and to activate the recruitment of new members.

The first Congress of the URO took place on May 18, 1909.  Maj. Gen. (r)  Nikola Bochev was elected as its President. The Balkan wars interrupted the process of establishment of the Union. The second Congress wasn’t held until June 1920, after an initiative of the Sofia’s reservists section. On the sixth Congress in 1924 it was reported that the Union includes 75 sections with more than 6000 members.

Over the years before the World War II the Union kept its activities. There were different fractions, but the Union saved its organizational integrity. During the war, the Union continued to work. 

On  Dec.1, 1944, after 37 years of history,  the URO was announced as a supporter of fascist policies and closed by the Minister of the Interior Anton Yugov. In the years of its existence, the Union has continuously defended the principles of patriotism, professional honor, dignity and respect to the traditions of the Bulgarian Army. During the wars that led our army, it practically validated its slogan "Bulgaria above all".

During the "Cold War" the Government changed several times its policy towards the reservists. It founded a "Committee for work with the officers in the reserve" in 1959. 

After the November 1989 changes arises the necessity of consolidation of the reservists in a national organization. An Initiative Committee including General Boris Karamfilov, Lt Gen. Atanas Rusev and Maj. Gen. Petko Nikolov was elected.  The reestablishing Congress held on Jan. 23, 1990 and founded The Reserve Officers and Noncommissioned Officers Union (RONU) leaded by Lt. Gen. Petar Stoyanov. On the second Congress in 1991 was announced that the RONU is the successor of the closed in 1944 Union of Reserve Officers and in 1945 Union of Reserve Noncommissioned Officers and this circumstance is reflected in the Statutes of the Union, adopted on its third Congress (1994). The sixth Congress of the Union (2005) adopted new rules of the Union, caused by the membership of Bulgaria in NATO. 

In 1997 the “National Association Security" became the first collective member of the RONU. Currently there are seven collective members. 

After the reestablishment of the Union nine Congresses have been held and four generals have been replaced as Presidents. On the 9-th Congress (2017) Gen. (r) Zlatan Stoykov was elected on the highest position of the RONU.

The Union started contacts with the administrations of the Ministries of Defense and Interior in 1990. They help to maintain the connections with the staff of the Bulgarian Army and of the National Security structures. RONU’s military-patriotic activities have an important contribution to the enlargement of its authority. The members involved in the maintenance and recovery of military monuments and cemeteries from 1878 to the present on the territory of the country and beyond our borders are enjoyed with pride and appreciation, also in building new monuments that perpetuate the glory of the Bulgarian army and the heroism of our forefathers in the protection of the territorial integrity of our country. 

The RONU has been accepted as a member of The Interallied Confederation of Reserve Officers (CIOR) since 2003 and of The International Advisory Committee of Organizations of Reserve Officers (IAC) since 2013.