Breen, a 1983 graduate of Fordham University, is currently[when?] in his 19th season as an NBA broadcaster, with some of those 19 taking place while Breen worked for NBC up until 2002, the network's last year as both an NBA and WNBA broadcaster. He is also the main voice for New York Knicks games on MSG Network. He first worked with the Knicks as a radio announcer for WFAN from 1992–97, when he was promoted to television play-by-play upon Marv Albert's firing following his infamous sex scandal. He later became Albert's backup upon his return in 1999, before finally becoming the lead play-by-play upon Albert's second dismissal in 2004. On February 8, 2006, with the departure of Al Michaels from the network, ABC announced that Breen would take over as the lead broadcaster for the NBA, including the NBA Finals. His broadcasting career started doing play-by-play for the Marist College Red Foxes basketball team in 1985. Other than his role as ABC's main play-by-play on Sundays, Breen usually works for ESPN on Fridays, and occasionally on Wednesdays, with the rest of his schedule reserved for MSG. He has also called college basketball games for ESPN as well.
When the Knicks made the 2011 NBA Playoffs, he did not call any of the games for MSG due to his involvement with ESPN and ABC; he did call Games 3 (with the MSG broadcasts handled by Kenny Albert) and 4 for ESPN and ABC, respectively.
In addition, he is also the voice of the NBA Elite series, beginning with NBA Elite 11, alongside his usual ESPN partners Mark Jackson and Jeff Van Gundy. However, the series was canceled indefinitely. He did voice along with Gundy in the NBA Live series beginning with NBA Live 13.
Breen has been a fixture on the radio as well. He began his professional radio career as a sportscaster on WNBC radio in the early 1980s, and frequently substituted for Dave Sims as host of "SportsNight" on the station. From 1989–2000, Breen did the sports segment on the WFAN and nationally syndicated Imus in the Morning talk/comedy radio show. Breen became noted for his deadpan delivery of false sports news, such as in the mid-1990s reporting that in the previous night's Mets game, "Félix Millán went 4-for-4 with 3 runs scored" (Millán retired in 1977).
2002 Eastern Conference Finals, Game 3 – Breen, with partner P. J. Carlesimo on NBC, called one of the greatest comebacks in NBA playoff history, as the Boston Celtics overcame a 25-point deficit to defeat the New Jersey Nets, 94–90. Breen's call:
And the Celtics have just overcome a 25-point deficit to beat the Nets! Give them credit, as they never gave up.
...The problem is, if Wallace is ejected, I'm not sure, he'd have to walk past the Pacer bench to go—Now Artest has jumped over the scorers' table, and is trying to get down to the bench! Artest is in the stands! Oh, this is awful! Fans are getting involved, Stephen Jackson's in the fans! Rasheed Wallace going into the stands! The security trying to somehow restore order! Fans and players are going at it, and the players are trying to help each other out! All the players now, they're jumping in there to try and get the other players out because the fans have come involved! Oh, what a sad scene, here at the Palace!
2006 NBA Finals, Game 5 – Calling his first NBA Finals, Breen was the voice of a classic and controversial NBA Finals game, which ended in overtime after a disputed foul and a botched time-out that cost the Dallas Mavericks a victory and helped propel the Miami Heat to a title.
2011 NBA Finals, Game 2 - Down by 15 points with just under 6:30 left in the game, the Dallas Mavericks came back to beat the Miami Heat in what Breen called "one of the most incredible comebacks in NBA Finals history". The Mavericks went on to win the championship.
2013 NBA Finals, Game 6 - LeBron James led a profound comeback in the fourth quarter against the Spurs, and erased a ten-point deficit. Ray Allen's three-point shot sent the game into over time, and the Heat eventually won in a thriller to send the series to a Game 7. Breen's enthusiastic call of Allen's three:
James catches, puts up a three, won't go! Rebound Bosh, back out to Allen, his three-pointer, bang! Tie game with five seconds remaining!
Carmelo Anthony's 62 point game—Breen had a very enthusiastic call for Carmelo's shot that took the record:
Anthony leans in, bank shot is good! Carmelo Anthony with the greatest scoring game in Knicks' history, he's got 62!