The Fourth Army fought in the Romanian Campaign of World War I, under the command of General Prezan.
The Fourth Army fought on the Axis side as part of the German Army Group B and later it fought on the Allies's side as part of the Soviet Second Ukrainian Front during World War II.
From late 1942 to early 1943, the Fourth Army was almost entirely destroyed during the Battle for Stalingrad. The Romanian Third Army suffered a similar fate.
In August 1944, the Red Army entered Romania after driving back Army Group South from the region. On August 23, Marshal Ion Antonescu was dismissed by King Michael I, and Romania declared war on Germany and Hungary some days later. The Soviets took control of the oilfields in the Ploieşti area, and the Romanian Army was used to fight German forces on the Eastern Front.
1944年8月，苏联红军击退了盘踞在罗马尼亚的德军南方集团军群，并进入罗马尼亚。8月23日安东内斯库元帅（Marshal Ion Antonescu）被罗马尼亚国王迈克尔（Michael）一世解职，几天后，罗马尼亚向德国和匈牙利宣战。苏军进驻后即控制了罗马尼亚的普洛耶什蒂（Ploieşti）地区的油田，而罗马尼亚军队则用来进攻德军的东线部队。
The Fourth Army became one of the Romanian armies fighting for the Red Army on the Eastern Front. In its campaign from August 1944 to May 1945, the Romanian Army lost some 64,000 men killed. The Fourth Army took part in Soviet offensives, notably at Prague in May 1945, which happened to be the last offensive it took part in World War II.
In the Prague Offensive, the Fourth Army, together with the Romanian First Army, Polish Second Army, and Soviet Second, and Fourth Ukrainian Fronts. Marshal Ivan Koniev, the commander of the First Ukrainian Front, was the main Soviet commander in the area. Together with Marshal Georgy Zhukov's First Byelorussian Front, Koniev had launched the great attack on April 16 that resulted in the fall of Berlin and Soviet victory on the Eastern Front.
The offensive started on May 6, a few days before the end of the war. German resistance in the east was now limited to small pockets scattered across Germany, Czechoslovakia, and Austria. The remnants of Army Group Center held the remaining German-controlled areas in the east. In the attack on Prague, German resistance was defeated in the city, and the Soviet, Romanian, and Polish forces entered the city on May 9. Czech partisans had been fighting the Germans there for a few days.
By May 11 and 12, all remaining German pockets of resistance in the east were defeated.
4th Infantry Division - HQs Cluj-Napoca
81st Mechanized Operational Brigade – Bistriţa
191th Infantry Battalion "Colonel Radu Golescu" – Arad
811th Infantry Battalion "Dragonii Transilvaniei (Transylvanian Dragons)" - Dej
812th Infantry Battalion "Şoimii Carpaţilor (Carpathians Hawks)" - Bistriţa
814th Tank Battalion – Turda
817th Mixed Artillery Battalion - Prundu Bârgăului
55th Anti-aircraft Missiles Battalion - Dej
405th Logistics Battalion – Bistriţa
15th Mechanized Territorial Brigade "Podu Înalt" - Iaşi
33rd Mechanized Battalion "Alexandru cel Bun" – Botoşani
151st Infantry Battalion "Războieni" - Iaşi
61st Mountain Troops Territorial Brigade "Virgil Bădulescu" - Miercurea Ciuc
22nd Mountain Troops Battalion "Cireşoaia"
24th Mountain Troops Battalion - Odorheiu Secuiesc 
26th Mountain Troops Battalion "Avram Iancu"
69th Mixed Artillery Regiment - Şimleul Silvanie
7th Artillery Battalion "General Vasile Danacu"
612th Anti-tank Artillery Battalion - Baia Mare
4th Logistics Brigade – Dej
43rd Transport Battalion
4th Engineer Battalion – Deva
52nd Engineer Battalion - Satu Mare
136th Bridges Battalion - Alba Iulia
50th Mixed Anti-aircraft Missile Regiment "Andrei Mureşianu" - Floreşti
55th Signal Battalion "Napoca" - Cluj-Napoca
317th Reconnaissance Battalion "Vlădeasa" - Cluj-Napoca
400th Logistic Support Battalion
498th Paratroopers Battalion – Bacău
72nd NBC Battalion - Huşi
202nd NBC Battalion – Sighişoara