Raúl Modesto Castro Ruz was born in Birán, Cuba.

In 1953, Raúl served as a member of the 26th of July Movement group that attacked the Moncada Barracks; he spent 22 months in prison as a result of this action.

The two Castro brothers with their army arrived on the outskirts of Santiago de Cuba and said their forces would storm the city at 6 PM 1 January if it did not first surrender. The commander (Colonel Rego Rubido) surrendered Santiago de Cuba without a fight. The war was over and Fidel was able to take power in Havana when he arrived on 8 January 1959.

During his exile in Mexico, he participated in the preparations for the expedition of the boat Grandma to Cuba. When the Granma landing failed and the 82 expeditionaries were detected by government troops soon after, Raúl was one of only 12 fighters who managed to reach a safe haven in the Sierra Maestra mountains, forming the core of the nascent rebel army (see the Cuban Revolution). As Fidel's brother and trusted right-hand man, and given his proven leadership abilities during and after the Moncada attack, he was given progressively bigger commands.

On 27 February 1958 Raúl was made comandante and assigned the mission to cross the old province of Oriente leading a column of guerrillas to open, to the northeast of that territory, the "Frank País Eastern Front". As a result of Raúl's "Eastern Front" operations, he was not involved in the pivotal Operation Verano (which came close to destroying the main body of fighters but ended up a spectacular victory for Fidel), but Raúl's forces remained active and grew over time.

On 26 June 1958, Raúl Castro's rebels kidnapped ten Americans and two Canadians from the property of Moa Bay Mining Company (an American company) on the north coast of Oriente Province. The next day rebels took hostage 24 US servicemen on leave from the United States naval base at Guantanamo Bay. This incident brought total kidnapped hostages to 36 (34 US and 2 Canadian citizens).

While Che Guevara and Camilo Cienfuegos were operating in Santa Clara, Fidel and Raúl's army laid siege to Maffo, capturing it on 30 December. Their victorious army then headed to Santiago de Cuba, capital of Oriente province.

In response to the victory by Che Guevara at the Battle of Santa Clara, the U.S.-backed President Fulgencio Batista fled Cuba in the early morning of 1 January 1959. After Batista's fall, Raúl had the task of overseeing trials and execution of scores (between 30 and 70) of soldiers loyal to deposed president Batista convicted of war crimes.

Castro married Vilma Espín, a former Massachusetts Institute of Technology chemical engineering student and the daughter of a wealthy lawyer for the Bacardi rum company, on 26 January 1959.

He was appointed Minister of the Revolutionary Armed Forces when it was founded in October 1959 and served in that capacity until February 2008.

Raúl Castro Ruiz was a member of the national leadership of the Integrated Revolutionary PO Organizations (established July 1961; dissolved March 1962) and of the United Party of the Socialist Revolution of Cuba (established March 1962; dissolved October 1965).

He served as a member of the Central Committee of the Communist Party of Cuba and Second Secretary of its Politburo from the Party's formation in October 1965.

He served as First Vice President of the Cuban Council of State of the National Assembly of People's Power and Council of Ministers when these were established in 1976.

On 31 July 2006, Fidel Castro's personal secretary, Carlos Valenciaga, announced on state-run television that Fidel Castro would provisionally hand over the duties of First Secretary of the Communist Party of Cuba (party chief), President of the Council of State of Cuba (head of state), President of the Council of Ministers of Cuba (prime minister), and Commander-in-Chief of the Armed Forces to Raúl Castro while Fidel underwent and recovered from intestinal surgery to repair gastrointestinal bleeding.

After assuming what was envisioned as a temporary control over the presidency in 2006, on 24 February 2008 Raúl Castro won election as the new President of the Council of State and President of the Council of Ministers during a legislative session held at Cuba's Palace of Conventions in Havana.

Raúl Castro became The First Secretary of the Central Committee of the Communist Party (in office since 19 April 2011).

On 24 February 2013 Cuba's parliament named Raúl Castro to a new five-year term as president and appointed Miguel Díaz-Canel as his first vice president. Castro announced that day that he would step down from power after his second term as president ended in 2018.

On 20 July 2015, Cuba and the United States officially resumed full diplomatic relations with sections of "Cuban interests" in Washington, D.C., and "U.S. interests" in Havana upgraded to embassies (The embassies had previously been dissolved in 1961 after Cuba became closely allied with the USSR).

Miguel Díaz-Canel took over as President of Cuba (President of the Council of State) on 19 April 2018. Raúl Castro remains First Secretary of the Central Committee of the Communist Party.