Ben Bella enlisted in the army again in 1940, believing that this would give Algerians an equal treatment. Consequently, he fought for the French during World War II, and he was even awarded twice. He received the ″Croix de guerre″ after manning an anti-aircraft post during the Nazi invasion in 1940. He was demobilised after the fall of France but joined a Free French regiment of Moroccan tirailleurs (infantry) with whom he saw Service throughout the Italian campaign. There, he was again awarded because of his bravery demonstrated at Monte Cassino, where he dragged one wounded CO to safety, assuming control of his battalion. For this,he was promoted to the rank of warrant officer, and he received the ″Médaille militaire″, the highest decoration of the Free French forces, directly from Charles de Gaulle.
On May 8, 1945, while France was celebrating Germany’s capitulation, big protests started to occur in the Algerian town of Setif. The cruelties of colonialism became worse during the wartime period, prompting more Algerian people to stand up against them. Protests turned to five days of rape and killing, and according to the official report deaths were more than 100 Europeans and around 1,500 Algerians. The anti-colonialists however put the number of Algerian deaths as being around ten thousand. This shocked Ben Bella and his Algerian companions, as they realized that they would not start receiving an equal treatment even after their services in war.
At the outbreak of the Algerian War in 1954, Ben Bella was based in Cairo where he had become one of the nine members of the Revolutionary Committee of Unity and Action which headed the Front de Liberation Nationale (FLN), founded on November that year, during a secret meeting of Algerian Leaders in Switzerland, in which they also ordered armed insurrection against the French colonists that would start the war between Algeria and France.
When Egyptian President Gamal Abdel Nasser brought Ben Bella to speak for the first time to an Egyptian audience, he broke into tears because he could not speak standard Arabic. Like many Arab Revolutionaries of the time, he would come to describe himself as a "Nasserist" and developed close ties to Egypt even before independence was achieved. Nasser's material, moral and political support of the Algerian movement would come to cause Nasser troubles, as it played a major role in France's choice to wage war on him during the 1956 Suez Crisis.
After Algeria's independence, Ben Bella quickly became more popular. In June 1962, he challenged the leadership of Premier Benyoucef Benkhedda; this led to several disputes among his rivals in the FLN, which were quickly suppressed by Ben Bella's rapidly growing number of supporters, most notably within the armed forces, whose chief was Houari Boumédiènne. By September, Bella was in control of Algeria in all but name. He was elected premier in a one-sided election on 20 September, which was recognized by the United States on 29 September. Algeria was admitted as the 109th member of the United Nations on 8 October 1962.
During his regime, he had political problems with former Leaders of the FLN, such as Mohammed Khider, Ferhat Abbas, Mohammed Boudiaf and Hocine Aït Ahmed. Ahmed founded the Front des Forces socialistes (Socialist Forces Front) (FFS) to confront Ben Bella and the others joined after being alienated by Ben Bella's dictatorial leadership. In 1963, the FFS called for an armed revolt against the regime. However, it had force only in the Kabylia region, and by the summer of 1964 the revolt was controlled and FFS Leaders were arrested.
In international relations, he had to maintain connections with the former colonial master France, and also accepted economic aid from both the U.S. and the Soviet Union, as each sought to move his regime into its orbit and into opposition to the other. Moreover, he wanted Algeria to be a leader country of the Third World liberation movements and of the Third World itself. For strengthening relations with other colonies and former colonies, Algeria joined the Non-Aligned Movement under Ben Bella’s regime, and he forged links with such African Leaders as Gamal Abdel Nasser, Kwame Nkrumah, Modibo Keita and Sekou Toure to aid rebel movements throughout Africa. He also established good relations with Fidel Castro, Che Guevara and Cuba; after his 1962 visit Cuba sent a health mission to Algeria, with doctors and medical help, and later sent weapons and Soldiers as aid during the Sand War against Morocco. He was awarded the title Hero of the Soviet Union on 30 April 1964.
His government finished suddenly when in June 1965, while he was planning to host an Afro-Asian international meeting, he was deposed in a bloodless coup led by Houari Boumédiène, his defense minister. He was held for eight months in an underground prison, then for the next 14 years lived under house arrest.
After being deposed in 1965, Ben Bella was sent to an underground prison where he was detained for eight months. After that, he was transferred to an isolated villa in Birouta, where he was placed under house arrest for 14 years. However, he was permitted a private life there, and in 1971 he married Zhora Sellami, an Algerian Journalist. Their meeting, was arranged by Ben Bella’s mother. They became religiously observant Muslims, and adopted two girls, Mehdia and Nouria. After Boumedienne's death in 1978, restrictions on him were eased in July 1979, and he was freed on 30 October 1980. Ben Bella briefly resided in France, but was expelled in 1983. He then moved to Lausanne, Switzerland, and launched the Mouvement pour la Démocratie en Algérie (MDA), a moderate Islamic opposition party, in 1984. In September 1990, he returned to Algeria, and in 1991 led the MDA in the first round of the country's abortive parliamentary elections. The MDA was banned in 1997.
In February 2012, Ben Bella was admitted to a hospital for medical checks. At the same time, a report circulated that he had died, but this was denied by his family.
After the events of Setif, Ben Bella returned to Algeria, reincorporating into its political life and into the opposition movement against the French regime. French authorities sent assailants with the intentions of assassinating him on his farm. The attempt to end his life failed, but Ben Bella’s farm was confiscated and he had to hide. After the Government election of Marcel-Edmond Naegelen, he became part of a group that thought democratic independence through peaceful means was something illusory. Together with Messali Hadj's and his party, he founded the Organisation Spéciale (OS), a paramilitary organization whose aim was to take up arms against the French colonial regime as quickly as possible. This was the immediate predecessor of the National Liberation Front. In 1949, he robbed a bank in Orán to gain funds for the organization, but he was eventually caught and sent to jail in Blida prison in 1951,sentenced to eight years imprisonment. He escaped soon afterwards, making his way to Tunisia and then to Egypt, reaching Cairo by 1952.