Ruben Spannaus was born May 31, 1913, in Loveland, Colorado, where his parents, Emma Schulenberg Spannaus and Edward Spannaus, had moved a few years earlier from Arlington, Minnesota. In 1920, the family moved to Woodland, California, where Ruben completed high school at age 16; he then enrolled in the University of California, Berkeley, in August of 1929, and graduated with honors in 1934. During summers and at other times during the school years, Ruben worked on farms and other odd jobs; he also learned carpentry and woodworking – skills he utilized all his life – from his father Edward, whose own father, Friedrich Spannaus, was a skilled craftsman trained in architecture in Saxony.
He entered Concordia Lutheran Seminary in St. Louis in 1934, and also participated in the Mission Society, teaching at the Niedringhaus mission in the slums of St. Louis. He later said that this is where he developed his interest in social ministry.  While here, he met the love of his life, Olive Wise. 
In 1936-37, he served his vicarage at Lodi, California, where many Midwesterners had moved during the Depression. The requirements listed in the Lodi congregation's application for a vicar were that the candidate do janitorial work, systematic mission work in the community, and be able to converse and preach in German as well as in English. Ruben excelled at all three.
Ruben graduated from Concordia Seminary in 1938. Because of the Depression, there were few calls, so Ruben went back to California and worked in a sugar beet factory, and within a few months he was invited to teach at Concordia College in Oakland, California, where he taught math and science, history, and other subjects, until late 1939. In late October, Ruben was offered a position serving a new mission in El Monte, California, by the Southern California Board of Missions. On December 23, 1939, with the blessings of the Mission Board, and after traveling back to St. Louis, Ruben was married to Olive Adelaide Wise. They subsequently had four children: Boots (1940), Edward (1943), Timothy (1946), and Fredric (1947). Ruben accepted a call a few months later from a congregation in Livingston, California. The call emphasized the mission responsibilities he would have, for which the Livingston congregation leaders obviously regarded Ruben as being well-suited; these included serving a mission in Merced, and serving as a volunteer chaplain at a sanitarium and at the Merced County Hospital. Ruben was ordained at Livingston on April 7, 1940.
A major concern during Ruben's tenure in Livingston was the forced relocation of Japanese farmers and farm workers – about one-third of the local population – to detention camps, because of fears induced by the war. Ruben protested this, along with the county ministerial association, but, as he later wrote, "we were unable to make an impression on the government."
In June of 1942, Ruben received a call to serve as Institutional Missionary for what is now Lutheran Ministry Services Northwest, serving residents of hospitals, jails, and other facilities in the greater Seattle area.
On September 13, 1942, Ruben was installed in his new position, and quickly began to establish volunteer chaplaincy programs at Harborview County Hospital and other facilities and institutions in the area. In 1944, Ruben served on the organizing committee for the creation of a pan-Lutheran social welfare agency, now known as Lutheran Community Services Northwest but then called Associated Lutheran Welfare, and in January 1945, he became its first Director.
In 1957, Ruben and family re-located to the Chicago area, where Ruben had been offered the position of Executive Director of the Lutheran Child Welfare Association (now known as Lutheran Child and Family Services) of Illinois. During his 21-year tenure, the agency was significantly expanded and its operations upgraded and modernized. Under his leadership the organization constructed a modern children's home to replace an aging and obsolete "orphanage," built new headquarters and created a network of satellite offices throughout the state. By the time he left after 21 years service, LCFS was recognized as a model family services agency.
In 1978, Ruben "retired," and he and Olive moved back to their favorite city, Seattle.
Throughout his professional career and in retirement, Ruben worked tirelessly at the state and national levels for improvements in the child welfare system and for issues of social justice. He twice served as chair of the Child Welfare League of America, and, in retirement, was a peer reviewer with the Council on Accreditation of Services for Families and Children. He served in leadership positions with United Way of King County and the Seattle/King County Area Council on Aging. Other "retirement" positions included business manager of Seattle Lutheran High School and Coordinator of the Lutheran-Roman Catholic Dialogue, as well as interim positions and preaching and teaching at Lutheran churches throughout the Seattle area. Ruben continued his chaplaincy work as long as he was able.