In 1952, Carter began his work with the US Navy's nuclear submarine program. He was sent to the Naval Reactors Branch of the Atomic Energy Commission in Washington, D.C. for three month temporary duty, while Rosalynn moved with their children to Schenectady, New York.
In March 1953, Carter began nuclear power school, a six-month non-credit course covering nuclear power plant operation at Union College in Schenectady. Carter's father died and he was released from active duty to allow him to take over the family peanut business. Carter left active duty on October 9, 1953.
He was in the inactive Navy Reserve until 1961, and left the service with the rank of lieutenant. His awards included the American Campaign Medal, World War II Victory Medal, China Service Medal, and National Defense Service Medal.
Carter's father, James died after having recently been elected to the Georgia House of Representatives. For a year, Jimmy, Rosalynn, and their three sons lived in public housing in Plains. Carter is the only U.S. President to have lived in public housing before he took office. Carter wanted to expand the family's peanut-growing business. His first-year harvest failed due to drought, however Carter wanted to open several bank lines of credit to keep the farm going. Meanwhile, he also took classes and read up on agriculture while Rosalynn learned accounting to manage the business's books. Though they barely broke even the first year, the Carters grew the business and became successful.
Carter, who was against racial segregation, was inspired to run for office over the racial tensions in the country. By 1961 he was a known member of the Plains community and the Baptist Church as well as chairman of the Sumter County school board. At the school board, Carter spoke against racial segregation in public schools.
In 1962, Carter announced his run for a seat in the Georgia State Senate. At first, the results showed Carter losing, but this was the result of fraudulent voting done by the Democratic Party chairman in Quitman County. Carter challenged the results; when fraud was confirmed, a new election was held, which he won.
Beginning in 1962, the town of Americus was the site of mass beatings of black protesters. Carter was quiet on the issue at first. He did speak up on a few divisive issues, giving speeches against literacy tests and against a change to the state constitution. At the time of President Kennedy's assassination, Carter was informed by a customer of his peanut business of the killing. Carter later called the assassination "the greatest blow that I had suffered since my father died".
Within two years, his connections in the state senate landed him on the state Democratic Executive Committee, where he helped rewrite the state party's rules. He became chairman of the West Central Georgia Planning and Development Commission.
When Bo Callaway was elected to the U.S. House of Representatives in November 1964, Carter wanted to run against him in the next congressional election. The two had fought over which two-year college would be expanded to a four-year college program by the state. Carter wanted it to go to his alma mater, Georgia Southwestern College, but Callaway wanted the funding to go to downtown Columbus.
Carter was re-elected in 1964 to a second two-year term. For a time in the State Senate, he chaired its Education Committee and also sat on the Appropriations Committee toward the end of his second term. Before his term ended he worked on a bill expanding statewide education funding and getting Georgia Southwestern a four-year program. The last day of the term, he announced his run for the United States House of Representatives.
At first, Carter ran for the Georgia's 3rd congressional district in 1966 against Bo Callaway. However, Callaway dropped out and decided to run for Governor of Georgia instead. Callaway had just switched from the Democratic Party to the Republican Party in 1964. Carter later decided to run for governor himself. In the Democratic primary, he unsuccessfully ran against the liberal former governor Ellis Arnall and the conservative segregationist Lester Maddox.
Governor Maddox was not allowed to run for a second consecutive term as governor in 1970. Former governor Carl Sanders became Carter's main opponent in the 1970 Democratic primary. Carter leaned more conservative than before during this primary election.
That September, Carter led Sanders in the first ballot by 49% to 38%, leading to a second round. Carter won the Democratic nomination with 59% of the vote compared to Sanders's 40%. In the general election, Carter was beat Republican Hal Suit winning 59% of the vote against Suit's 40%.
Carter became the 76th Governor of Georgia on January 12, 1971. In his inaugural speech, he said that "the time of racial discrimination is over. ... No poor, rural, weak, or black person should ever have to bear the additional burden of being deprived of the opportunity for an education, a job or simple justice". "Time" ran a story on the progressive "New South" governors elected that year in a May 1971 issue. The cover of the magazine had an illustration of Carter.
Lester Maddox, who Carter replaced as governor, became lieutenant governor. Richard Russell Jr., then President pro tempore of the United States Senate, died in office during Carter's second week in office. Carter appointed David H. Gambrell, state Democratic Party chair, to replace Russell's in the Senate.
Carter wanted to expand the governor's authority while making the state government easier to run. He supported a bill allowing him to propose executive restructuring and to force a vote on it. The plan was submitted in January 1972, but had a negative reception in the legislature. But after two weeks of negotiations, it was passed. He merged about 300 state agencies into 22 agencies.
In an April 1971 televised appearance, Carter was asked if he was in favor of a requirement that candidates for Governor and Lieutenant Governor of Georgia would have to run on the same ticket. He replied, "I've never really thought we needed a lieutenant governor in Georgia. The lieutenant governor is part of the executive branch of government and I've always felt—ever since I was in the state Senate—that the executive branches should be separate". In July 1971, during an appearance in Columbus, Georgia, Carter announced his plans to create a Georgia Human Rights Council that would work toward solving issues in the state ahead of any potential violence.
In January 1972, Carter wanted the state legislature to give funding for an Early Childhood Development Program along with prison reform programs and 48 million in pay taxes for nearly all state employees. In April 1972, Carter traveled to Latin and South America for a possible trade deal with Georgia. Carter said that he had met with Brazilian President Emílio Garrastazu Médici. Many compared him to President Kennedy.
Carter increased the number of black state employees, judges, and board members. He placed portraits of Martin Luther King Jr. in the capitol building, even as the Ku Klux Klan protested the ceremony. During a televised appearance with Governor of Florida Reubin Askew in January 1973, Carter said he supported a constitutional amendment to ban busing to make the process of desegregation in schools faster. He co-sponsored an anti-busing resolution with George Wallace at the 1971 National Governors Conference. which Carter also hosted. Carter signed a new death penalty law after the United States Supreme Court rejected it. Carter later regretted supporting the death penalty, saying, "I didn't see the injustice of it as I do now".