Nasution had a long career in and out of leadership in Indonesia. He was a major military leader during the struggle for independence, commanding the Siliwangi division in West Java. In 1952, he was dismissed from his command during a period of conflict between the army and Sukarno. By 1955, he was back in favor. In 1958, during the time of the PRRI and Permesta rebellions, Nasution first suggested the idea that would later be called "dwifungsi", the "dual function" of the military, the idea that the military should have social and even political obligations as well as defense duties.

In the early 1960s, Nasution was an opponent of the growing power of the PKI. He barely escaped the coup attempt of September 30, 1965 with his life, jumping over the wall to the Iraqi ambassador's residence next door. Nasution had investigated Suharto for corruption in the 1950s; later, in 1980, Nasution was a signer of the "Petition of Fifty" that criticized Suharto as President.

The "dwifungsi" concept was Nasution's idea to find a middle way between democracy, which some people in the late 1950s felt had failed, and outright military dictatorship, which Nasution wanted to avoid. But in practice, military units began to skim money from companies that Sukarno had nationalized, to collect customs and tolls, even to engage in smuggling--especially since Sukarno's government was able to pay them less every year. While some military men built roads, schools and mosques in their civil service, for others used their position as a military man in civil service to engage in corruption.

In the 1950s, "dwifungsi" was seen as a way to avoid giving total power to the military. By the 1990s, the "dwifungsi" concept was criticized by some as giving far too much influence to the military.