Gena Branscombe was born in Picton, Ontario, Canada, in 1881. She entered the Chicago Musical College in 1897 to study piano with Rudolph Ganz and composition with Felix Borowski. In 1901 and 1902, she won gold medals for her pieces. Between 1903 and 1907, she taught piano in Chicago, leaving to join the faculty as head of the piano department at Whitman College, Walla Walla, Washington. Her compositional interests led her to leave Whitman in 1909 to study with Engelbert Humperdinck in Berlin. She returned to Ontario in 1910, where she married John Ferguson Tenney. The couple moved to New York City, where she pursued her career while also starting a family. She had four daughters between 1911 and 1919.

Branscombe studied choral conducting during the 1920s in New York with Chalmers Clifton and Albert Stoessel, of the Oratorio Society of New York. She was very active in working for the equality of women in the field of music. In 1928 she was elected president of the Society of American Women Composers. The same year received the annual prize given by the League of American Pen Women for her large-scale choral drama Pilgrims of Destiny; she wrote the text and music. In 1932, she received an honorary Master of Arts degree from Whitman College.

In 1933, she founded the Branscombe Choral [sic], formerly the American Women's Association Choral. She conducted the sixty-member women's choir for twenty-one years. Branscombe wrote new works for the group and commissioned works by other women composers. The Choral gave radio broadcasts, performed for commuters in Penn Station and Grand Central Station, and presented annual concerts at Town Hall.

Branscombe's compositional output includes some 150 art songs, piano and chamber music, a few orchestral works, and a large body of choral pieces. Her most significant large-scale instrumental work is Quebec Suite from her unfinished opera, The Bells of Circumstance. Among her many choral compositions for women's voices, she wrote Coventry's Choir (1944) on the bombing of Coventry Cathedral during World War II. Her hymn, Arms that Have Sheltered Us, was adopted in 1960 by the Royal Canadian Navy. At age ninety-two, Branscombe composed Introit, Prayer, Response, and Amen, commissioned by Riverside Church, New York City. She died on July 26, 1977, in New York City.