Struck by Portland's lack of a civic chorus, C. Robert Zimmerman decided to start one at the end of World War II. Of the 150 singers who auditioned in August 1945, he selected 80. They met to rehearse on September 5, and at the next rehearsal the singers chose the organzation's permanent name, the Portland Symphonic Choir. The choir's mission was "to sing the choral masterworks with excellence and passion and to engage, educate, enrich and inspire its members and the community." Its first major concert was in December 1945, with a performance of Handel's Messiah.

Portland Symphonic Choir was incorporated as a nonprofit organization in 1947-1948, and Zimmerman took a season's leave to study choral conducting with Robert Shaw at Tanglewood in the Berkshires and at the Juilliard Institute in New York City. He led the choir until 1961, followed by Frank Holman (1963-1973), David Wilson (1974-1978), Bruce Browne (1979-2001), and Steven Zopfi (2003-2017). Other conductors led PSC for at least a season: Karl Ernst (1947-1948), Donald Thulean (1961-1962), Jacob Avshalomov (1962-1963), and Deborah Glaze (2001-2003).

In December 1947, the choir performed the Genesis Suite, a work by seven contemporary composers, with the reorganized Portland Symphony Orchestra, which had been inactive since 1938. It was the beginning of a productive collaboration that continues in the twenty-first century (the Portland Symphony Orchestra became the Oregon Symphony Orchestra in 1967). The choir and orchestra performed together in the Oregon centennial celebration at the state capitol in February 1959 and in a tribute to slain President John F. Kennedy in December 1963.

In the summers of 1952 through 1955, Portland Symphonic Choir produced fifteen light operas in the Holladay Bowl, an outdoor project conceived by Zimmerman. The Bowl was constructed in a pit that had been excavated in the 1920s for a Lloyd Center luxury hotel that was never built. The amphitheater, which had a rotating stage, had been constructed by volunteers in 1952 and now lies under the Lloyd Cinemas parking lot.

The choir has partnered with many organizations, including the Portland Chamber Orchestra, the Portland Youth Philharmonic, the Portland Opera, the Salem Symphony, Portland State University ensembles, Portland ballet companies, the Boston Pops, the Dave Brubeck Quartet, and the Cascade Festival Orchestra. It established the Symphonic Serenaders (1951-1974), a chamber choir, the Portland Symphonic Girlchoir (1989), and the Portland Boychoir (1994).

Portland Symphonic Choir has toured extensively, giving concerts in such places as Belgium, Germany, France, Estonia, Russia,  Australia, and the Czech Republic. It premiered works by Richard Moffatt (1959), Tomas Svoboda (1976), Tibor Serly (1978), Salvador Brotons (1994), Steven Paulus (1999), Bryan Johanson (1996, 2000, 2005), and Judith Lang Zaimont (2007). Notable recordings include the Victoria Mass for Four Voices (1958, RCA Victor), the Johanson Lux Aeterna (2007, PSC), and the Rachmaninoff All-Night Vigil (2009, PSC).