In Relic, D'Agosta is described as heavyset and balding, wearing an ill-fitting suit and chomping on an unlit cigar. D'Agosta is Italian-American and a native New Yorker. He sees himself as a regular, working-class guy. He is known for his profanity, which Pendergast describes as "colorful".
As a police officer he is competent and respected by his men. His short temper and dislike of bureaucracy frequently put him in conflict with his superiors.
Despite a career investigating crimes, D'Agosta is still squeamish around human remains. He embarrassed himself in Relic by vomiting at a particularly gruesome crime scene. Special Agent Pendergast commended him on not having lost all his humanity. D'Agosta is also frequently uncomfortable at autopsies.
Beginning in Reliquary, D'Agosta developed an on-again/off-again relationship with police Lieutenant (later Captain) Laura Hayward. The two split up for a time as Hayward felt that D'Agosta was going too far to help Pendergast, at the expense of his own career and well-being. They patched up their relationship and got engaged at the end of Two Graves, and were soon married, spending their honeymoon in Hawaii.
D'Agosta had been a police officer for at least 22 years as of the start of Relic. He held the rank of lieutenant and was the homicide detective in charge of the investigation when two young boys were found murdered in the basement of the New York Museum of Natural History. He soon met FBI Special Agent Aloysius Pendergast, who had come up from the New Orleans office to investigate the killings, which were similar to an unsolved case in the New Orleans area.
Pendergast and D'Agosta worked together extremely well and became good friends during and after the Museum Beast Murders case. D'Agosta admired Pendergast's Sherlock Homes-like powers of deduction and Pendergast admired D'Agosta's bravery, competence, and common touch.
After the events of Reliquary, D'Agosta retired to Canada to write crime novels under the pseudonym "Campbell Dirk". While in Canada he divorced his wife and became estranged from his son. He eventually returned to the United States and took a job as a sergeant with the Southampton Police Department.
D'Agosta teamed up with Pendergast and Laura Hayward again in Brimstone, to investigate a series of murders involving Satanic rituals. He later rejoined the New York Police Department at his old rank of Lieutenant.
In Dance of Death and The Book of the Dead, D'Agosta first helped Pendergast elude capture when he was a fugitive from the police, and then helped him break out of a federal prison. With D'Agosta's help Pendergast was able to clear his name and defeat his criminally insane younger brother, Diogenes.
When Pendergast set out to find the truth behind his wife Helen's death in Fever Dream, D'Agosta took a leave of absence from the NYPD and set off to help. He accompanied Pendergast to Africa and then helped him investigate various locations in the American South. While leaving Penumbra Plantation, D'Agosta was shot in the back with a large-caliber sniper rifle. The shot was meant to kill Pendergast but badly wounded D'Agosta, who lay in the hospital for several weeks. He required surgery and a replacement heart valve but survived. While D'Agosta was laid up with his injuries, his girlfriend Laura Hayward grudingly agreed to help Pendergast continue the investigation.
In Cold Vengeance, D'Agosta returned to duty on a desk job. He met Pendergast's young protégé Corrie Swanson when Corrie came looking for Pendergast's whereabouts. D'Agosta looked into the matter and was shocked to learn of Pendergast's apparent death in an accident in Scotland. D'Agosta went to Scotland and found Pendergast, alive and in hiding after being severely wounded by his brother-in-law Judson Esterhazy. Pendergast had learned that Helen was not dead after all, but had gone into hiding following a plot on her life.
With D'Agosta's help, Pendergast and Helen were briefly reunited, but a shootout followed and Helen was kidnapped. Pendergast's pursuit of the kidnappers opened the novel Two Graves.
D'Agosta stayed behind in New York but helped Pendergast by communicating with local police departments. After a climactic standoff in Mexico, Helen was killed. Pendergast returned home utterly dejected and refused to leave his apartment. D'Agosta worried for his friend and attempted to help, but Pendergast was inconsolable.
D'Agosta returned to active duty when he was assigned to investigate a series of murders in New York City hotels. Working with the FBI, he quickly discovered that the killer was leaving small pieces of his own body behind at the crime scenes. The killer seemed to have a preternatural ability to evade capture and left taunting messages at each crime scene. The case was interesting enough to pull Pendergast out of his stupor, and the two worked together on the case.
Pendergast and D'Agosta learned enough to predict where the next killing would occur, but arrived too late to stop it. Pendergast was removed from the case following the revelation that the kidnapper was a son that Pendergast was unaware he had. The two had a falling-out over D'Agosta's disclosure of the information, and Pendergast pursued his son back to Nova Godoi, Brazil. Upon returning to New York, Pendergast helped D'Agosta ferret out a mole in the NYPD, and they resumed their friendship.
As the case wound down in New York, D'Agosta reflected that his career and his personal life were finally back on the right track. On Christmas Eve, he took Laura Hayward to the bar where they'd had their first date. As D'Agosta struggled to propose, Hayward smiled and graciously accepted. They planned their wedding for May 29th of the following year. Pendergast hosted a lavish dinner reception in their honor, and the newlyweds honeymooned in Hawaii.When Pendergast went missing after investigating a private case in Massachusetts, D'Agosta paid a few visits to Constance Greene, who had accompanied Pendergast and returned alone, disconsolate. Almost a month later, D'Agosta received an urgent phone call from Pendergast himself, requesting that he check on the Riverside Drive residence. There, he came face-to-face with Diogenes Pendergast, in the process of what appeared to be an abduction of Constance. D'Agosta held Diogenes at gunpoint while directing Constance to safety, but she suddenly knocked him unconscious with a priceless Ming vase. He awoke in the hospital, and groggily recounted the adventure to Hayward and a visibly agitated Pendergast.
After being released from the hospital, he returned to the Riverside Drive mansion to supervise the removal of the crime scene tape from the reception hall, at the request of Mrs. Trask.
- D'Agosta, who considers himself Italian by heritage, is semi-fluent in Neopolitan, a dialect of Italian not widely spoken outside of its city of origin, Naples. While traveling in Italy with Pendergast during the events of Brimstone, Vincent attempted to speak the "Italian" he learned from his parents, and was nonplussed to learn from Pendergast that modern Italian is actually based on Florentine, which is why the Italians to whom he was attempting to speak regarded him with confusion and suspicion.