In 1967, having made the decision not to enter the priesthood,[3] Barthelemy returned to New Orleans and became an administrative assistant in the office of Total Community Action.

Backed by COUP, Barthelemy was elected in 1974 to one term in the Louisiana State Senate from District 4;[6] he was the first African-American to serve in that body since Reconstruction.

While he served in the Legislature, he also joined Xavier University as assistant director of the Urbinvolve Program and as an instructor in the Department of Sociology and became an adjunct faculty member in the Applied Health Sciences Department, Maternal and Child Health Section, of Tulane University.

In 1979, Barthelemy was elected to the state Senate, defeating a white incumbent who had held the seat for sixteen years.

[12] Eliminated in the primary was former state Representative Sam A. LeBlanc, III, who finished with a strong 25 percent of the vote.

Federal government revenue sharing to municipalities had been progressively reduced from 1981 onwards, and had ended by the time Barthelemy took office in 1986.

This plan involved cutting costs, raising fees, and privatizing operations, in the course of which over 1,000 city workers lost their jobs.

[21] Taking a less hands-on approach to economic development than his predecessor, Barthelemy preferred to let the private sector be the primary engine of growth.

[22] Though Barthelemy took a pro-business stance, his unfocused, laissez-faire approach to attacking the city's problems was harmful in the post-Oil Bust period; it was during his and his successor's mayoralties that New Orleans lost much of its remaining attractiveness as a center for corporate white collar employment.

As recently as the late 1970s and early 1980s, downtown New Orleans had experienced a building boom, with multiple office towers constructed to house the headquarters, or large regional offices, for companies such as Freeport-McMoRan, Pan American Life Insurance, Exxon, Chevron, Gulf Oil, Amoco, Mobil, Murphy Oil and Texaco.

Out of the above group, only Shell and Pan American Life Insurance remain as significant employers in downtown New Orleans today.

The contract, won by Boeing, resulted in thousands of jobs created at that company's chosen assembly site, Huntsville, Alabama.

More disappointment followed the creation of the Metrovision regional economic development partnership, as that body largely failed to diversify or attract additional investment to Metro New Orleans' economy.

In the wake of the Oil Bust, however, the Barthelemy administration most forcefully advocated for the continued development of New Orleans' tourist and convention industry.

Several high-profile wins occurred, including attracting the Republican National Convention to the city in 1988 and the NCAA Final Four tournament in 1993.

[23] In administering city government, Barthelemy managed to gradually eliminate the $30 million budget deficit he inherited in 1986, but his methods of raising revenue - attempting to impose an "earnings tax" on the personal income of suburbanites who worked within the city limits, legalization of a land-based casino and riverboat gambling - were controversial.

Other notable narratives of the Barthelemy administration included the visit of Pope John Paul II to New Orleans in 1987, the passage of the controversial "anti-discrimination" ordinance affecting the membership in Carnival krewes, an unsuccessful, city-sponsored effort to redevelop Louis Armstrong Park into a Tivoli Gardens-style recreation park/amusement center, an unsuccessful proposal to construct a new international airport in New Orleans East, in what later became the Bayou Sauvage National Wildlife Refuge, the post-World's Fair gentrification and redevelopment of the downtown Warehouse District, and the securing of funding for a new sports arena next to the Superdome.

Plans to re-use portions of the former Canadian Pavilion of the World's Fair, including its IMAX theater, as a new Louisiana Science Museum came to nothing, however.

National trends were also unfavorable to cities during Barthelemy's mayoralty; New Orleans was far from alone in grappling with economic stagnation and rising crime.

At his son's graduation ceremony from Brother Martin High School, it was announced that he would be receiving the "Mayor's Academic Scholarship to Tulane University."

By the end of the week, the story was the talk of the state, and it was revealed that in addition to the Mayor, all members of the Louisiana Legislature could grant scholarships to Tulane University.

Louisiana legislators were permitted to award the scholarships to anyone they saw fit, provided that the nominee was a bona fide citizen and resident of the district or parish and "shall comply with the requirements for admission established"[29] by the university's board.

Through further investigation, it was revealed that politicians regularly gave these scholarships to their own family members and to the children of political allies.

"[30] Barthelemy was quite self-aware with regard to his temperament, viewing it as a strength and once remarking that, "People tend to underestimate me because I don't bang my fist on the table and jump up and scream...but I know how to get the job done and that's always been my aim — to get things done.".

[34] Currently, Sidney Barthelemy is serving as the Director of Governmental Affairs for Historic Restoration, Inc. (HRI Properties), a real estate development group based in New Orleans.