Sarah Ann Turner ("Annie") was born on August 26, 1827, in Sandy Springs, Ohio, to John G. and Elizabeth Smith Turner. Her family valued education a great deal, and she was therefore educated despite her gender. At age 12, her first poem was published, and by age 20, she married William Wittenmyer. She took care of Sally, her husband's daughter from his first marriage. She and her husband had a son, Charles, together. Of her four children, only Charles Albert lived past early childhood. Her husband died when she was only 33-years-old, leaving her with two children to care for. Early in her career, Wittenmyer focused on education. She opened the first tuition-free school in Iowa. Wittenmyer not only provided a free education to children, but also provided meals and clothes those in need. She also set up Sunday schools, and she used her poetry skills to write hymns for the children. One of the hymns she wrote is "A Wonderful Joy."

At the start of the Civil War, Wittenmyer dedicated her life to relief work. As secretary of the Soldiers' Aid Society, she visited troop encampments and organized a statewide system of local aid societies to promote the collection of hospital supplies. Wittenmyer is said to have done the most to provide care for the sick and wounded in the Union army. General Ulysses Grant, commander of the Union army, said, "No soldier on the firing line gave more heroic service than she did." Wittenmyer noticed the poor conditions in which sick soldiers were expected to recover, and she decided to do something about it. Many letters were written to army officials urging them to offer aid. She also encouraged women to send food to the wounded. She was put in charge of all hospital kitchens for the Union army. She donated much time and money providing good food, clothes, and nurses to aid wounded soldiers. After the war, Wittenmyer worked to locate homes for the orphaned children from the war. As a result, there is an orphanage named after her in Davenport, Iowa.

In September 1862, Wittenmyer was appointed to the Iowa State Sanitary Commission, and it was the first time a woman was distinctively named in an Iowa legislative document. In 1874, she was elected the first president of the National Woman's Christian Temperance Union, an organization devoted to the removal of alcohol from American life. In the five years of her presidency, the WCTU established over 1,000 local branches, taught almost 5,000 children about temperance, and enrolled over 100,000 men in reform clubs. Despite her busy life, she found time to write. History of the Women's Temperance Crusade was published in 1878, and Women of the Reformation as published in 1884. In 1889, Wittenmyer became President of the Women's Relief Corps, and had homes built for retired nurses, widows, and mothers of veterans. In the early 1890s, while bedridden from an injury, she wrote her autobiography, Under the Guns.

Wittenmyer died of a cardiac asthma attack on February 2, 1900, in Sanatoga, Pennsylvania. She was 72-years-old.