Rachel Katharine Lasheck was born in Iowa City, Iowa on March 23, 1891, the youngest of three daughters of John and Mary Becker Lasheck. Known to her family as "Baby" and to her friends as "Rosy", she changed her name to Katharine La Sheck early in her professional singing career. Her sisters were Adelaide Lasheck Burge, who was Dean of Women at the University of Iowa from 1921 to 1942, and Ruth Lasheck Freyder. La Sheck attended elementary school in Iowa City and began high school there in 1904. Her family moved to Allegheny, Pennsylvania, when she was in ninth grade and later moved to Revere, Massachusetts, where she graduated from high school in 1909. La Sheck studied voice professionally and began her career soon thereafter, performing in recital and in ensemble with the Ideal Quartet, The College Girls (1911-1915), and the Marigold Quartet (1915-1920). The quartet members danced, acted, and played a variety of musical instruments. Booked by the Redpath Chautauqua, they performed widely on the Chautauqua circuit and were enthusiastically received. In 1913 and 1914 the College Girls travelled to Panama to entertain Americans working on the canal, and performed, too, on the cruise ships of the United Fruit Company Steamship Service. In 1917 La Sheck toured with the Murray Opera Company in the production of "Dorothy", a light opera. La Sheck also performed dramatic roles in theatrical presentations for the Redpath Chautauqua.

After The Marigold Quartet disbanded in 1920, La Sheck settled in Buffalo; during the time she lived there she performed with the New York Light Opera Singers, in oratorio groups, and as a soloist. From 1935 to 1943 she was an entertainer and hostess at the Broadcast Corporation of Buffalo. La Sheck returned to Iowa City periodically to visit family and to present recitals. In 1943, after her sister Adelaide Burge retired from the University, she moved there permanently and taught voice at The University of Iowa School of Music from 1944 to 1959. She died June 1, 1971.