Temple De Hirsch Sinai, the first and largest Jewish Reform congregation in Seattle, was founded in 1899 by a group of 70 area families. Originally named Temple de Hirsch after Jewish philanthropist Baron de Hirsch, the congregation was renamed after merging with Temple Sinai of Bellevue, Washington, in 1971.

The location for the first proposed sanctuary of Temple De Hirsch Sinai was Boylston Avenue and Marion Street in Seattle, and a cornerstone containing the congregation's founding documents and other time capsule materials was laid there in 1901. However, after rapid growth of the congregation warranted a larger facility, this site was abandoned in favor of Union Street and 15th Avenue, where the first sanctuary was completed in 1907. In 1924 the adjacent Temple Center was built to house the new Religion School and other subordinate organizations. Steady growth required further expansion, and in 1951, an addition for the school was built next to the Temple Center. By 1959, sufficient funds had been raised to build a new sanctuary, and although many Jewish families were moving into suburban areas, the congregation chose to keep a central location in downtown Seattle. A new temple with a 1000-member capacity was built on the corner of 16th Avenue and Pike Street in 1960, located on the same block as the original sanctuary, which was eventually demolished in 1993.

The first spiritual leader of Temple De Hirsch Sinai, Rabbi Theodore Joseph from Lancaster, Pennsylvania, oversaw the establishment of the religious school in 1899, which began with an enrollment of 65 students.

Rabbi Samuel Koch, senior rabbi from 1906 to 1942, established Temple De Hirsch Sinai as an important and steadily expanding congregation. Particularly committed to the growth and development of the Religion School, he welcomed all students, regardless of whether their parents were Reform Jews. Koch was also civically active, with memberships in or associations with numerous Seattle agencies and organizations. In 1909 he established the congregation's newsletter, Temple Tidings , initially a weekly and later a monthly publication. Koch became Rabbi Emeritus on his retirement.

Rabbi Raphael Levine, senior rabbi from 1942 to 1970, developed many ecumenical programs, including "Challenge," a television program he co-hosted with a Catholic priest and a Protestant minister. Addressing theological issues from different schools of religious thought, "Challenge" ran on local station for 14 years, appearing first on KOMO-TV and later on KING-TV. Levine was the founder of Camp Brotherhood, a religious, educational, and cultural center for Christians and Jews, and a co-founder of Camp Swig, an educational and recreational camp for Jewish youth. He served on boards and committees for many social service organizations and related groups, and founded the Pacific Association of Reform Rabbis.¶ Rabbi Earl Stanton Starr, senior rabbi from 1970 to 2001, perpetuated the temple's long tradition of community service and outreach through his involvement in a wide variety of organizations, boards and committees.

Samuel Goldfarb, composer of the well-known Chanukah song "I Have a Little Dreidl," was music director of Temple De Hirsch Sinai from 1930 to 1968. He employed a system of training his singers based on the farm system in baseball, advancing children into higher choir "leagues" as they matured. Under Goldfarb's direction, the temple's choirs were considered among the finest in the country.

Long-standing organizations within Temple De Hirsch Sinai include the Sisterhood, formerly the Ladies Auxiliary, which was established a few months after the congregation was founded, and the Brotherhood, formerly the Temple Men's Club, established in 1920. Both groups organize, sponsor, and promote services and activities for the Temple De Hirsch Sinai congregation and the Jewish community.