Daneyko was drafted in the 1st round (18th overall) in the 1982 NHL Entry Draft, the first pick of the New Jersey Devils after the franchise relocated from Colorado. He spent several seasons in the minors before getting drafted, and played for the Yorkton Terriers of the Saskatchewan Junior Hockey League, as well as the Great Falls Americans, Spokane Flyers and Seattle Breakers of the Western Hockey League. He then split time between the Devils and the Maine Mariners of the American Hockey League before being called up full-time for the 1985-86 NHL season.
Upon his arrival in the NHL, #3 established himself as a stay-at-home defenceman, and soon won fans over with his gritty and self-sacrificing play. Daneyko was also known for his missing front teeth, lost after he was hit in the mouth by a puck. His gap-toothed smile was well known not only by Devils supporters, but by hockey fans around the world. As a player who had spent all of his NHL career with New Jersey, Daneyko was nicknamed "Mr. Devil".
Daneyko racked up over 2,200 penalty minutes in his career, finishing a season with over 200 PIM five times. Daneyko was never known as a high-scoring defenceman, and set a record by playing in 255 consecutive regular-season games without scoring a goal. In fact, in his highest-scoring season, 1989-90, he scored only six goals and 15 assists en route to a 21-point season. Five seasons he scored no goals at all. However, Daneyko's effectiveness was not measured by how many pucks he put in the net, but by how many pucks he kept out. Daneyko was used primarily as a shadow defenceman, and often got physical in front of the net if a forward parked himself in the crease looking for a rebound.
In the late 1990s, Daneyko struggled with alcoholism but General Manager Lou Lamoriello and Devils owner Dr. John McMullen stood by him and checked him into rehab.  Daneyko recovered and played every game of New Jersey's successful 2000 playoffs, winning the Bill Masterton Trophy in 2000 for his perseverance.
Along with Scott Stevens, he was part of a tough Devils defensive corps that won three Stanley Cups in 1994-95, 1999-2000, and 2002-03. From the team's first playoff game while in New Jersey in 1988, Daneyko played in every playoff game until Game 4 of the 2003 Quarterfinals. He also was scratched in the first six games of the 2003 Finals, but looking for a spark Coach Pat Burns inserted Daneyko into the lineup for Game 7. As a reward to his devotion of the team, and a hint of his impending retirement, Daneyko took the ice for the final shift of the Devils' Game 7 victory over the Mighty Ducks of Anaheim, which clinched their third Stanley Cup victory in 2003.
|Kansas City Scouts/Colorado Rockies/New Jersey Devils first-round draft picks|
|Scouts: Paiement • Dean|
Rockies: Gardner • Beck • Gillis • Ramage • Gagne • Cirella
Devils: Trottier • Daneyko • MacLean • Muller • Wolanin • Brady • Shanahan • C. Foster • Guerin • Miller • Brodeur • Niedermayer • Rolston • Smith • Pederson • Sharifijanov • Sykora • Ward • Damphousse • Van Ryn • Gomez • Ahonen • Hale • A. Foster • Parise • Zajac • Bergfors • Corrente • Tedenby • Josefson