The father of Danny Messer (played by Carmine Giovinazzo) was a member of the Italian Mafia and thus Danny grew up in an environment in which he was constantly surrounded by criminal activity on the one hand and law enforcement on the other hand. Due to the activities of his father, (not just) his family was more or less constantly monitored by the police and as Danny grew older, this surveillance extended on him.

Little is known about his childhood and youth, as well as about his educational journey. In college, Danny Messer played baseball and was very successful, soon regarded as a rising star. But then it came to a fight in a bar, during which he was injured, which meant the end of the envisaged baseball career.

Mac Taylor has brought Danny Messer to the CSI: NY team and Danny mostly works very hard to meet the expectations of his superior. Because of his often impulsive nature, Danny gets into trouble from time to time, perhaps due to the fact that he has some very individual ideas of morality. These originate from his childhood in which he was repeatedly exposed to the various views of law breakers and law enforcement officials. Danny Messer is indeed a complicated character, but a very dedicated investigator who follows every clue and leaves no stone unturned.

The dismissal and subsequent murder of his colleague, Detective Aiden Burn, hit him very hard. So when Lindsay Monroe arrives to strengthen the team, he quickly makes friends with her. The two private investigators are always working on something together, leading over time to them falling in love. Danny is also the one who nicknamed Lindsay Montana, which is how she is not called every now and then.

After the young son of his neighbour was shot while Danny was with the boy on the way, he also had a brief affair with the mother of the little one. This affair was born out of grief of the two, with Danny still blaming himself for the death of the boy. Even if he could not have prevented the crime, he kept telling himself that he was not paying enough attention to the child.

Danny and Lindsay later become a couple, and they get married and move in together after Lindsay gets pregnant. When the whole team is at a bar after the funeral of Detective Don Flack's girlfriend, Jessica Angell, there is a wild shooting inside the bar through the large glass window.

Danny is thereby hit by a bullet and is the only one to be seriously injured. In the hospital, it turns out that there is a possibility that he could remain paralyzed from the hip down. Danny is initially bitter about his situation and his wife cannot calm him down.

After hearing different opinions, he begins to fight for his recovery. Through a lengthy and painful physical therapy, he succeeds by and by to move his legs. Meanwhile, he is working for the lab on CSI: New York mostly limited to the office. Even while he is confined to a wheelchair, Danny Messer struggles to investigate, being transported to the scenes.

He is not supported by Mac Taylor when he is summoned by an anonymous caller to a secluded meeting. The anonymous woman who promises information about the crime is shot in the presence of the two detectives, so that the perpetrator initially also remain unknown.

Finally, Danny succeeds to rise from a wheelchair permanently. One night, his wife, Lindsay, wakes up alone in their bed, looking for him and finds her husband in the nursery. There he stands with their child in his arms next to the crib - the wheelchair a few meters away.