"Famines are not natural phenomena, they are catastrophic political failures," it said in a statement.
"The world was too slow to respond to stark warnings of drought, exacerbated by conflict in Somalia, and people paid with their lives. These deaths could and should have been prevented, and such a shocking death toll must never be allowed to happen again."
World leaders meeting in London next week to discuss the situation in Somalia "must take steps to ensure that this was Somalia's last famine," Oxfam said.
This means investing in long-term development, creating jobs, supporting farmers and pastoralists, and ensuring properly trained security forces to help achieve the "just and sustainable peace" the country so badly needs, it said.
Somalia has lacked an effective central government since 1991, with portions of the Horn of Africa nation left lawless.
Its shaky transitional government, backed by African Union peacekeepers, has been battling Islamist guerrillas for years.