Homma was born on Sado Island, in the Sea of Japan off Niigata Prefecture. He graduated in the 14th class of the Imperial Japanese Army Academy in 1907, and in the 27th class of the Army Staff College in 1915.
Homma had a deep respect for, and some understanding of, the West, having spent eight years as a military attaché in the United Kingdom. In 1917 he was attached to the East Lancashire Regiment, and in 1918 served with the British Expeditionary Force in France, being awarded the Military Cross.
From 1930 to 1932, Homma was again sent as a military attaché to the United Kingdom, where his proficiency in the English language was useful. He was also assigned to be part of the Japanese delegation to the Geneva Disarmament Conference in 1932 and served with the Press Section of the Army Ministry from 1932 to 1933. He was given a field command again, as commander of the IJA 1st Infantry Regiment from 1933 to 1935, and was promoted to command the IJA 32nd Infantry Brigade from 1935 to 1936.
In 1937, Homma was appointed aide-de-camp to Prince Chichibu, a brother of Emperor Shōwa. With him, he made a diplomatic tour in Europe which ended in Germany. There he attended the Nuremberg rally and met Adolf Hitler, with whom the prince tried to boost relations, following the Anti-Comintern Pact of 1936. He then served as the commander of the Taiwan Army of the Imperial Armed Forces, and composed the lyric of the military song "Taiwan Army". Yamaguchi Yoshiko ("Lee Shiang Lan" in Chinese) was invited to sing the song to boost Taiwanese morale.
With the start of the Second Sino-Japanese War, Homma was appointed commander of the IJA 27th Division in China from 1938 to 1940 and directed the blockade of the foreign concessions in Tientsin, where he led the negotiations with the British. After the fall of Nanking, he declared publicly that "unless peace is achieved immediately it will be disastrous". Homma was removed from his position at the front lines, and reassigned to become commander in chief of the Taiwan Army District from 1940 to 1941. He was promoted to lieutenant general in July 1938.
With the start of the Pacific War, Homma was named commander of the 43,110-man IJA 14th Army and tasked with the invasion of the Philippines. He ordered his troops to treat the Filipinos not as enemies but as friends, and respect their customs and religion. In one instance, on his approach to Manila, Homma stopped his columns and ordered the men to clean up and tighten formations, knowing that unkempt soldiers are more likely to loot and rape.
This liberal approach towards Filipino civilians earned him the enmity of his superior, General Count Hisaichi Terauchi, commander of the Southern Army, who sent adverse reports about Homma to Tokyo from his headquarters in Saigon. There was also a growing subversion within Homma's command by a small group of insubordinates, under the influence of Colonel Tsuji Masanobu. In Homma's name, they sent out secret orders against his policies, including ordering the execution of Filipino Chief Justice José Abad Santos and attempted execution of former Speaker of the House of Representatives Manuel Roxas, which Homma found out about in time to stop.
Homma failed to give credence to the possibility that a retreat into the Bataan Peninsula by Filipino-American forces might succeed in upsetting the Japanese timetable. By the time he recognized his mistake, his best infantry division had been replaced by a poorly trained reserve brigade, greatly weakening his assault force. Rather than waste his men in furious frontal assaults, he tried to outmaneuver the American forces. This brought criticism from superiors who believed he had been "contaminated" by Western ideas about conserving the lives of his men.
Worried about the stalled offensive in Luzon, Hirohito pressed Army Chief of Staff Hajime Sugiyama twice in January 1942 to increase troop strength and launch a quick knockout on Bataan. Following these orders, Sugiyama put pressure on Homma to renew his attacks. The resulting Battle of Bataan commencing in January 1942, was one of the most intense in the campaign. However, the deteriorating relationship between Homma and Sugiyama led to the removal of Homma from command shortly after the fall of Corregidor, and he was thereafter commander of the 14th Army in name only. The New York Times erroneously reported prior to the fall of Bataan that Homma was replaced by General Yamashita, and that Homma had committed suicide.
The Imperial General Headquarters regarded Homma as not aggressive enough in war (resulting in the high cost and long delay in securing the American and Filipino forces' surrender), and too lenient with the Filipino people in peace, and he was subsequently forced into retirement in August 1943. Homma retired from the military and lived in semi-seclusion in Japan until the end of the war.
After the surrender of Japan in mid-September 1945, the American occupation authorities arrested Homma and extradited him to the Philippines where he was tried by an American tribunal on 48 counts of violating international rules of war relating to the atrocities committed by troops under his command during the Bataan Death March.
It is not clear whether Homma ordered the atrocities that occurred during the march, but it is clear that his lack of administrative expertise and his inability to adequately delegate authority and control his men helped to enable the atrocities. After American-Filipino forces surrendered the Bataan Peninsula, Homma turned the logistics of handling the estimated 25,000 prisoners to Major-General Yoshitake Kawane. Homma publicly stated that the POWs would be treated fairly. A plan was formulated, approved by Homma, to transport and march the prisoners to Camp O'Donnell. However, the plan was severely flawed, as the American and Filipino POWs were starving, were weak with malaria, and numbered not 25,000 but 76,000 men, far more than any Japanese plan had anticipated.
At his trial, Homma also claimed that he was so preoccupied with the plans for the Corregidor assault that he had forgotten about the prisoners’ treatment, believing that his officers were properly handling the matter. He claimed that he did not learn of the atrocity until after the war, even though his headquarters were only 500 feet from the route of the march.
On February 11, 1946, Homma was convicted of all counts and sentenced, “...to be shot to death with musketry”. Homma was executed by firing squad by American forces on April 3, 1946, outside Manila.
There have been various claims and charges that Homma's trial was unfair or biased. Contemporary sources stated the following:
Associate Justice Frank Murphy, in dissent of denial of a hearing by the U.S. Supreme Court on a rule of evidence, stated, "Either we conduct such a trial as this in the noble spirit and atmosphere of our Constitution or we abandon all pretense to justice, let the ages slip away and descend to the level of revengeful blood purges."
Homma's chief defense counsel, John H. Skeen, Jr., stated that it was a "highly irregular trial, conducted in an atmosphere that left no doubt as to what the ultimate outcome would be."
General Douglas MacArthur in his review of the case wrote,
If this defendant does not deserve his judicial fate, none in jurisdictional history ever did. There can be no greater, more heinous or more dangerous crime than the mass destruction, under guise of military authority or military necessity, of helpless men incapable of further contribution to war effort. A failure of law process to punish such acts of criminal enormity would threaten the very fabric of world society.