After the 1965 Watts riots, Ryan took a job as a substitute school teacher to investigate and document conditions in the Los Angeles area.

Shortly after the airstrip shootings, 909 members of the Jonestown settlement died in a mass murder–suicide by drinking cyanide-laced Flavor Aid.

He taught English at Capuchino High School, and chaperoned the marching band in 1961 to Washington, D.C., to participate in President John F. Kennedy's inaugural parade.

[10] Ryan served as a delegate to the Democratic National Convention in 1964 and 1968[4] and held his Assembly seat until 1972, when he was elected to the United States House of Representatives.

[19][20] Ryan once told Dick Cheney that leaking a state secret was an appropriate way for a member of Congress to block an "ill-conceived operation".

[22] In 1978, reports of widespread abuse and human rights violations in Jonestown at the Peoples Temple, led by cult leader Jim Jones, began to filter out of its Guyana enclaves.

[23][24] After reading an article in the San Francisco Examiner, Ryan declared his intention to go to Jonestown, an agricultural commune in Guyana where Jones and roughly 1,000 Temple members resided.

His decision was also influenced both by the Concerned Relatives group, which consisted primarily of Californians, as did the Temple, and by his own distaste for social injustice.

[27] In a later article in The Chronicle, Ryan was described as having "bucked the local Democratic establishment and the Jimmy Carter administration's State Department" in order to prepare for his own investigation.

Ryan traveled to Jonestown with 17 Bay Area relatives of Peoples Temple members, several newspaper reporters and an NBC TV team.

Ryan's stated position was that a "settlement deep in the bush might be reasonably run on authoritarian lines"[31] but that its residents must be allowed to come and go as they pleased.

"[31] On November 14,[32] Ryan left Washington and arrived in Georgetown, the capital of Guyana, 150 miles (240 km) from Jonestown, with his congressional delegation of government officials, media representatives and some members of the "Concerned Relatives.

[34] For three days, Ryan continued to negotiate with Jones's legal counsel and held perfunctory meetings with embassy personnel and Guyanese officials.

[33] On November 17, Ryan's aide Jackie Speier (who became a Congresswoman in 2008), the United States embassy Deputy Chief of Mission Richard Dwyer, a Guyanese Ministry of Information officer, nine journalists, and four Concerned Relatives representatives of the delegation boarded a small plane for the flight to Port Kaituma Airport, a few miles outside of Jonestown.

The smaller six-seat Cessna was taxiing to the end of the runway when one of its occupants, Larry Layton, opened fire on those inside, wounding several.

[32] That afternoon, before the news became public, the wife of Ryan's aide William Holsinger received three threatening phone calls.

[44] On March 3, 1987, Layton was sentenced to concurrent sentences of life in prison for "aiding and abetting the murder of Congressman Leo Ryan,"conspiracy to murder an internationally protected person, Richard Dwyer, Deputy Chief of Mission for the United States in the Republic of Guyana," as well as 15 years in prison on other related counts.

Ryan's body was returned to the United States and interred at Golden Gate National Cemetery in San Bruno, California.

[48] Ryan's younger sister Shannon said she was surprised both by the number of supporters who attended the funeral and by the "outgrowth of real, honest sorrow".

"[60] Near the end of the memorial service, parents of those who had died in Jonestown stood to honor and thank Ryan for giving his life while trying to save their children.

After the service ended, mounted police escorted the family and friends into Foster City's Leo J. Ryan Memorial Park.

[60] The same year, his daughter Erin Ryan, an aide to Speier, attended a memorial for those who died at Jonestown, held at the Evergreen Cemetery in Oakland.

[31] For the 30th anniversary, Speier sponsored a bill to designate the United States Postal Service facility at 210 South Ellsworth Avenue in San Mateo, California, the "Leo J. Ryan Post Office Building".

[70] In 2012, National Geographic's Seconds From Disaster aired the sixth-season episode "Jonestown Cult Suicide", which recreated Ryan's assassination.