During World War II the Imperial Japanese Army entered the province and Nueva Ecija was taken in 1942. In March 29, 1942, under the leadership of Luis Taruc the Hukbalahap (Hukbo ng Bayan Laban sa Hapon-People's Army Against the Japanese) was organized in Sitio Bawit, Barrio San Julian in the town of Cabiao. It was perceived to be the military arm of the Partido Komunista ng Pilipinas (Communist Party of the Philippines), that brought about the beginning of the early organized resistance of the Pilipino people. In 1945, combined American and Filipino soldiers liberated Nueva Ecija with the recognized guerillas continuing to harass the Japanese at every opportunity. When Filipino soldiers of the 21st, 22nd, 23rd, 25th and 26th Infantry Division of the Philippine Commonwealth Army and the 2nd Infantry Regiment of the Philippine Constabulary was re-invading launches to entering liberated the province of Nueva Ecija and helping recognized guerrilla resistance fighter units, the Hukbalahap Communist guerrillas and the American troops against the Japanese Imperial forces during the Invasion of Nueva Ecija. On January 30, 1945 American Army Rangers, Alamo scouts and Filipino guerillas conducted a raid to liberate Allied civilians and prisoners of war in Cabanatuan, this was successful with over 516 rescued. By January 31, 1945, the liberated civilians and POWs reached Talavera, the rescue is commemorated in Talavera.
The province was named after the old city of Écija in Seville, Spain.
In 1896, Nueva Ecija became one of the first provinces to revolt against Spanish rule, and one of the provinces which declared its independence in 1898.