PFLAG is a national LGBTQ+ activism organization whose mission is to support, educate, and advocate for LGBTQ+ people and their families. PFLAG was founded by Jeanne Manford in 1973 in New York, New York. In response to her son Morty Manford's mistreatment by the police during a Gay Activists Alliance protest, she wrote a letter to the New York Post and marched with her son in the 1972 New York Pride Parade, carrying a sign that read "Parents of Gays Unite in Support for Our Children." On March 11, 1973, Jeanne and her husband Jules hosted the first meeting of what was then known as Parents of Gays (POG) at the Metropolitan-Duane United Methodist Church in Greenwich Village. Throughout the 1970s, similar support organizations began to form in other parts of the country.

One such organization was founded in October of 1978 in Houston by Annella Harrison, who was the mother of a gay son named Patrick McIlvain. The Houston group was originally named Family and Friends of Gays (FAFOG). During the events of the 1979 National March on Washington for Lesbian and Gay Rights, members of these various advocacy groups around the country met in Washington D.C., including Annella Harrison. This convergence was the first big step toward forming a national organization. By 1980, the organization now known as Parents FLAG or P-FLAG began distributing educational information to local communities nationwide, and in 1982, the Federation of Parents and Friends of Lesbians and Gays, Inc., which represented about 20 groups at the time, was incorporated in California and granted nonprofit, tax-exempt status.

The Houston chapter officially changed its name to Parents FLAG in November of 1983 and was incorporated as a tax-exempt 501(c)(3) in February of 1993. PFLAG Houston grew steadily over time, from an average monthly meeting attendance of about 30 members in the early 1980s to an average monthly meeting attendance of 125 people, 250 paid members, and a newsletter mailing list of about 700 people by 1995. The group produced and distributed educational resources, organized around political topics affecting the LGBTQ+ community, and held and participated in community meetings and events. PFLAG Houston hosted "Healing the Hurt" conferences at University of Houston in the 1990s to train and inform educators, counselors, and law enforcement about how to support the LGBTQ+ community. They launched two billboard campaigns, a METRO bus advertising campaign, and television PSAs to warn about the dangers of hate speech and violence and to garner support and understanding for the LGBTQ+ community in Houston. PFLAG Houston produced "Always My Kid" with Houston TriAngle Productions, which premiered in Houston in 1994. In 1996, PFLAG Houston organized a road trip called Moms and Dads Go To Washington to raise awareness and show support for ENDA (The Employment Non-Discrimination Act), proposed legislation that would prohibit discrimination in hiring and employment on the basis of sexual orientation. A documentary film called "Claiming America's Promise" was produced about the trip. PFLAG Houston regularly participates in the Houston Pride parade; 14 PFLAG members have served as grand marshals, including founder Annella Harrison, and the group has been honored as the Organizational Grand Marshal twice.

Like the group's name, PFLAG's mission and inclusivity has evolved over time. In the 1980s, PFLAG National organized to oppose Anita Bryant’s anti-gay movement and the U.S. military’s efforts to discharge lesbians from service. In the 1990s, they worked on Safe Schools legislation and Title IX, and drew attention in opposition to the Religious Right after Pat Robertson threatened to sue any station running ads from PFLAG's "Project Open Mind" whose message linked hate speech with hate crimes and LGBTQ+ teen suicide. In 1993, PFLAG added the word "Families" to its acronym and included bisexual people into its mission, and in 1998, they officially brought transgender people into their mission as well. PFLAG has organized around marriage equality, ending "Don't Ask, Don't Tell," supporting LGBTQ+ youth, including addressing teen homelessness and suicide, fighting to end gay conversion programs, and opposing legislation that condones discrimination under the guise of religious freedom. In 2007, they launched the "Straight for Equality" initiative, a national outreach and education program to provide resources for allies who may not have a family or friend connection to the LGBTQ+ community in order to expand the organization's efforts to include even more people in the equality movement. In 2014, PFLAG dropped the acronym "Parents, Families, and Friends of Lesbians and Gays" and became simply PFLAG to more accurately reflect the intersectionality and inclusivity of the organization's members, mission, and work.

PFLAG Houston experienced membership decline in the early 2000s, and forward-looking members worked to pivot their outreach to families and friends of transgender individuals as gender identity issues gained more visibility. This is a large part of their current membership and outreach focus. They celebrated their 40 year anniversary on October 13, 2018 at Resurrection Metropolitan Community Church. PFLAG Houston currently holds monthly meetings at the Montrose Center, as well as smaller weekly support groups virtually and in person, and operates a helpline phone number and email address. They continue to partner with other local LGBTQ+ organizations, like HATCH, the Houston LGBTQ+ Political Caucus, and Houston Pride for Houston community events and outreach.