Danielle Rose Melnick is a New York City-based Defense Attorney who has been practicing for more than 20 years. A well-established, high profile litigator, she regularly goes up against the toughest, most powerful prosecutors in the Manhattan District Attorney's Office. For years, she was a thorn in the side of both Benjamin Stone and Jack McCoy. She has had an affectionately competitive friendship with the latter since the early days of their careers. She later moves to Chicago and is elevated to the position of Judge.
An idealistic, utterly professional workaholic, Melnick is so dedicated to her job that she often makes the lives of her opponents in the DA's office miserable. 
Much like McCoy, she is so zealous in her job that she will bend (but never break) trial laws to win a case. 
She sometimes risks being put in contempt of court for antagonizing a judge. 
The series has revealed nothing about her personal life.
While Danielle is willing to defend her clients to the best of her ability, at times she is shown to be disgusted by them and what they have done on a personal level. After she unwittingly helped her client continue his killing spree, Danielle freely admitted to hating him for it, but refused to turn on him legally even though it would've helped Danielle herself out. On another occasion, after being presented evidence that her client lied to her, Danielle demanded the truth out of him, stating that otherwise he would have to find a new lawyer.
While she is often at odds with Jack McCoy, the two have an affectionately competitive friendship. After Danielle was facing legal trouble for helping her client despite special orders from a judge which inadvertently helped him continue his killing spree, McCoy bent the rules to clear Danielle's name, something he described as "helping a good buddy."
Melnick was very nearly disbarred in a case in which she was representing a white supremacist accused of murdering a Defense Attorney. Angered by the gag order the trial Judge had put on her client, she passed along an address to one of the man's associates, assured that it would produce evidence that could clear him; unbeknown to her, however, it was actually the address of one of the terrorist's intended targets, who was soon murdered. She was arrested and charged as an accessory. She was mortified by what her client had done, but refused to break attorney-client privilege, even if it meant she would go to prison. Ironically, all her sacrifice was on behalf of a client who hated her for being Jewish.
McCoy, who was reluctant to prosecute his old friend, ended up saving her by lying to the man, telling him that Melnick had confessed to unwittingly helping him, and that he would go to prison for life unless he admitted that she hadn't known what he was going to do with the information. Melnick was cleared of all charges, but was shot soon after by one of her former client's followers. (L&O: "Open Season")
Melnick eventually recovered from her injuries and returned to her practice. She used a cane, but told Jack that her doctor said by this time next year, she'd be "dancing the night away". (L&O: "City Hall")
Melnick returned to defend Jacob Reese, a fanatically religious man who murdered his daughter's teacher and burned down a church to cover it up. Reese claimed he did it out of fear that his victim's teachings would cause God to strike his daughter down and Melnick presented a religious defense, something she got the judge to accept. Privately, Melnick admitted to McCoy she didn't like the defense, but it was the only one out of ten possibilities that she offered Reese that he accepted. Its indicated that she leaked the situation to the press to put pressure on McCoy. After it turns out that Reese's daughter has an STD, Melnick threatens to quit if he won't tell her the truth and it comes out that Reese's daughter lied about who she had sex with. Reese agrees to plead to all of the charges and McCoy tells Melnick he is going to seek a penalty of 25 years to life. Departing, Melnick promises to see him around. (L&O: "Good Faith")
- Patricia Blaine (L&O: "Aria")
- Dr. Alex Merritt (L&O: "Helpless")
- Laura Bauer (L&O: "Golden Years")
- Leslie Harlan (L&O: "Hot Pursuit")
- Judith Sandler (L&O: "Survivor")
- Matthew O'Dell (L&O: "Disappeared")
- Alice Simonelli (L&O: "Punk")
- Harvey Bower (L&O: "Collision")
- Randall Wylie (L&O: "Judge Dread")
- Julian Pruess (L&O: "Open Season")
- Peter Rubin (L&O: "City Hall")
- Kevin Boatman & Robbie Howell (L&O: "America, Inc.")
- Jacob Reese (L&O: "Good Faith")
- Parker Gaffney (CI: "To the Boy in the Blue Knit Cap")
- People vs. Dylan Oates (CJ: "Fake")
- According to one of the episode scene cards in the episode "Judge Dread", Danielle Melnick’s office is located on 408 Park Avenue.
- Law & Order (13 seasons, 13 episodes):
- Law & Order: Criminal Intent (1 season, 1 episode):
- Chicago Justice (1 episode):
- Season 1: "Fake"