The Third Army faced the Yugoslavian First Army. By the time the Hungarians crossed the border and finally attacked, the Germans had been attacking Yugoslavia for over a week. As a result, the Yugoslavs put up little resistance to the Hungarians. Units of the Hungarian Third Army advanced into a triangular shaped area known as the Baranya-triangle between the Danube River and the Drava River. The Hungarians suffered few casualties in this invasion. As a result of participating in the invasion of Yugoslavia, Hungary regained Bácska and Baranya.
From 25 March to 15 April 1944, the Hungarian VII Army Corps was involved in the Battle of Kamenets-Podolsky pocket. The Hungarian VII Army Corps was to become part of the Hungarian Third Army in August.
On 30 August, the Hungarian Third Army was mobilized to defend Hungary against the relentless advances of the Soviet 2nd and 4th Ukrainian Fronts. The Chief of Staff of the Hungarian Armed Forces, Colonel-General János Vörös, ordered this army of nine weak, undermanned, and underequipped reserve divisions to attack west of the Hungarian Second Army (which was mobilized at the same time). The Third Army was to then cross Arad and the Maros Valley and occupy the mountain passes of Transylvania. This attack failed.
On 6 October, in the opening stages of the Battle of Debrecen, the Hungarian Third Army was badly mauled near Arad. Very quickly, the army was scattered near the town of Kecskemét. Rodion Malinovsky's 2nd Ukrainian Front attempted a pincer maneuver to encircle Army Group Fretter-Pico. The 2nd Ukrainian Front's southern pincer sliced easily through the Hungarian Third Army. This southern pincer was spearheaded by Soviet General Issa Pliyev's Mobile Group Pliyev. Later, in the same battle, Mobile Group Pliyev was encircled and badly mauled by Army Group Fretter-Pico (Armeegruppe Fretter-Pico). The northern pincer was stalled and turned back by veteran German panzer forces. The Hungarian Second Army was an integral part of the victorious German-Hungarian Armeegruppe Fretter-Pico.
The Order Of Battle in October 1944 was as follows:
The Hungarian Second Army was disbanded on 1 December 1944, after the Battle of Debrecen, and its remaining units were transferred to the Third Army.
From 29 December 1944, the Hungarian capital city, Budapest was under siege. In the Battle of Budapest every available Hungarian unit was employed in the defense of the capital. After great loss, the city was unconditionally surrendered on 13 February 1945.
Between 16 March and 25 March 1945, most of what was left of the Hungarian Third Army was surrounded and destroyed about forty kilometers to the west of Budapest. The army was destroyed by the Soviet 46th Army as it advanced towards Vienna.  But, even after this, the Hungarian Third Army did not totally cease to exist. Some remnants remained and they fought on. Fighting as they went, they moved progressively westward to southern Austria. The army was not officially disbanded until 8 May 1945, the end of the war. That is when the last commander of the Hungarian Third Army, Lieutenant General József Heszlényi, surrendered.