Janet Rosenberg was born in Chicago, Illinois, on October 20, 1920. After high school, she attended Wayne State University and the Cook County Nursing School. In 1942, she met Cheddi Jagan at a party hosted by a mutual friend. He was a Guyanese dentistry student at Northwestern University whose grandparents had immigrated to Guyana from India. Both were involved in radical politics, and they married the following year against the objections of her family.

After Cheddi’s visa expired in 1943, he returned to Guyana (then British Guiana). Janet followed soon after. Cheddi set up a dental surgery practice, with Janet working as his assistant. The couple quickly became involved with local politics and the Guyanese labor struggle, and Janet became a member of Guyana’s first union, working with labor leader Hubert Critchlow to organize domestic workers to strike for labor rights. Janet’s early political work in Guyana also included co-founding the Women’s Political and Economic Organization and the Political Affairs Committee in 1946. The couple's first child, Cheddi Jagan, Jr., was born in 1949.

In 1950, Janet co-founded the People’s Progressive Party (PPP) with Cheddi and trade union leaders Ashton Chase and Jocelyn Hubbard. The PPP was Guyana’s first multi-racial political party. In addition to serving as the party’s general secretary, Janet was also the first woman to be elected to the Georgetown City Council. Three years later, Janet was elected to the House of Assembly as the deputy speaker. American newspapers dubbed her the “second Eva Peron.” Janet sent a Western Union telegram to her parents that read, "Cheddi, myself and Party won overwhelming victory."

The 1953 elections in Guyana were the country’s first under universal suffrage. Although voters elected Cheddi as their chief minister, the British, fearful of the first Marxist leaders in the Western Hemisphere, ousted the PPP from office after only 133 days. In 1955, following the birth of Cheddi and Janet’s second child, Nadira, the couple was jailed as political prisoners.

The 1957 elections once again elected Cheddi as chief minister, and Janet as Guyana’s minister of labor, health and housing. Among her accomplishments were establishing health centers, maternity and child welfare clinics and improving wage and work conditions. Although the PPP was in office during this time, the party’s power was minimal, as the British still controlled the country’s government. In 1963, Janet became minister of home affairs, a post she later quit out of frustration over British control.

The early 1960s were turbulent times in Guyana, both economically and politically. In 1962, rioters tried to force the PPP out of office, and the American government continued to instigate unrest that led to the 1964 “reign of terror,” which uprooted, killed and injured thousands of Guyanese. When bombs were planted at PPP headquarters, Cheddi and Janet decided to send their daughter Nadira to live in the United States, and Janet was forced to keep a low profile. As she explained in THUNDER IN GUYANA, “In the '60s I could not be seen for years. I couldn't be seen or they would start attacking, burning, killing. I had to just lie low for a long time.”

Guyana finally won independence from the British in 1966, but by this time the PPP’s government had been replaced by the People’s National Congress (PNC), led by Forbes Burnham, a former PPP chairman who had since split with Cheddi and Janet. During Burnham’s 25-plus years in office, Guyana accumulated the worst foreign debt in the hemisphere and banned open elections. By the 1980s, half of Guyana’s population had fled the country. Janet continued her political work, editing the PPP-backed newspaper the Mirror and writing several children’s books about Guyana’s struggle for independence, and was elected opposition member of Parliament in 1973, 1980 and 1985.

In 1992, Guyana held its first free and fair elections in almost three decades, and with her husband elected president, Janet became the country’s first lady. In 1997, after Cheddi’s death, she became Guyana’s first woman president and commander-in-chief.