Greg Meffert, the technology wunderkind who played a starring role in the first real scandal of Mayor Ray Nagin’s administration and then turned state’s evidence after he found himself in legal quicksand, will be sentenced in federal court Thursday by U.S. District Judge Eldon Fallon.

Meffert, 49, who faces a maximum of eight years in prison under a plea deal, will be hoping that his testimony at Nagin’s trial in February — and his even more crucial turn on the witness stand in 2011 against erstwhile pal Mark St. Pierre — will persuade Fallon to give him substantially less time behind bars. Federal prosecutors will likely argue strongly on his behalf.

But Fallon may prove a tough audience. When he sentenced St. Pierre to 17½ years in prison, Fallon agreed with the technology vendor’s lawyer that St. Pierre was not the ringleader of the bribery scheme that sent him to jail, suggesting that the real culprit was Meffert.

Perhaps more than anyone apart from the mayor himself, Meffert embodied both the shining promise and the sour aftertaste of the Nagin administration.

Meffert and Nagin didn’t know each other before Nagin’s surprising, dark-horse election in 2002. Meffert joined the transition team, inspired by the new mayor’s talk of doing business differently and of getting away from the crony contracting practices that had long defined City Hall. He took a job as the city’s first chief technology officer, promising to bring the latest Silicon Valley innovations into a musty civic apparatus.

Meffert fulfilled at least some of that promise, upgrading analog phone and computer systems and overhauling the city’s appallingly bad website. In an act of quiet rebellion, he posted the city’s property tax rolls online, allowing people to see for the first time the absurd breaks many homeowners and businesses were getting, and indirectly, at least, sparking reform.

But he also played fast and loose with the rules that dictate how government work is doled out. Frustrated with the city’s in-house staff, he contracted out most of the tech work to a group of friends, led by St. Pierre. He did it without seeking bids or quotes, an arrangement he eventually got Nagin to bless through an executive order.

Over time, he grew increasingly close to Nagin, buying a house next door to him and flying the Nagin family to Hawaii to accompany the Mefferts on a family vacation. At City Hall, as Nagin’s circle of aides shrank, Meffert became more and more powerful.

By the time Hurricane Katrina struck in August 2005, the power seemingly had gone to his head. Meffert began calling himself “deputy mayor,” a position that didn’t exist, and a portfolio that had grown before the storm expanded even further, with the tech chief exerting influence over a wide range of departments.

As federal aid poured in, he opened the spigot of city money, funneling millions of dollars of work to favored contractors. He helped himself to an armed driver, who was paid the $75 hourly salary of a tech worker, at considerable taxpayer expense.

When his pals at Imagine Software, St. Pierre’s firm, bought a 57-foot yacht and christened it the Silicon Bayou, Meffert bragged to anyone who would listen that it was his — and it was, in fact, his to use when he wanted. That arrangement raised questions about how deeply Meffert’s interests were intertwined with those of the contractors he oversaw — questions that were largely answered when a civil lawsuit brought by a jilted crime-camera vendor revealed that the contractors had given Meffert a large expense account while he was still in his city post and paid him nearly $700,000 for “consulting” work shortly after his 2006 departure from City Hall.

Meffert; his wife, Linda; and St. Pierre were all charged in a 63-count indictment in 2009. Linda Meffert was accused of participating in the scheme by taking $38,000 in bribe payments hidden as accounting work.

While Greg Meffert, as a high-level city official, seemed to be the feds’ primary target, it was the Mefferts rather than St. Pierre who chose to cut a deal. Under it, Linda Meffert was allowed to attend a diversion program rather than plead guilty, and Greg Meffert had to admit that all of the payments from St. Pierre were kickbacks for the work he had steered to his friend, not earned income. He pleaded guilty to one count of conspiracy to commit wire fraud and bribery, and one count of filing false tax returns.

Meffert also had to agree to help the feds make other cases, and he delivered on that promise. He was the star witness for the government in St. Pierre’s 2011 trial, memorably telling a jury that St. Pierre paid strippers to come aboard the yacht and perform sex acts on both men and other members of their clique. His testimony helped clinch a guilty verdict on all 53 counts.

Earlier this year, Meffert again had a long turn on the witness stand, this time helping to convict his old boss and neighbor, Ray Nagin.

The old braggadocio was gone. Meffert, who has moved back to his hometown of San Antonio, was the picture of humility, his face haggard and worn, as he told prosecutors that Nagin knew St. Pierre was paying for his trips to Hawaii and Jamaica and was providing cellphones for his children.

Nagin sought to shrug it off, suggesting that a man who had testified otherwise on several other occasions shouldn’t be believed, and that Meffert was just doing anything he could to please prosecutors.

When asked if Meffert was a liar, Nagin responded: “He lied a lot of times. To the feds, and the FBI and in his civil case. I think Meffert lied a lot. He’s quite a storyteller.”

Follow Gordon Russell on Twitter, @gordonrussell1.