The Mavericks had several players coming into the free agency. Brandan Wright's option for another year was exercised on June 23. On July 1, 2012, the Mavs exercised the option on Vince Carter to sign him for the season.
Their main target was signing Deron Williams, who was under contract with Brooklyn until last year. They met with Williams on July 2 but he signed a five-year extension later with Brooklyn.
The Mavs started their regular season at the Los Angeles Lakers and their new formed team. They took the lead in the second quarter and never looked back, at the end it was a 99–91 victory and the season started off the right foot. Despite leading by eight at the break, the Mavericks fell in their first back-to-back this season to the Jazz 94–113. In their home opener against the Charlotte Bobcats the Mavericks blew them out by 27 with O. J. Mayo scoring 30 and the team going 16 of 25 from behind the arc. Mayo added another 30+ game and Darren Collison got his second straight double-double in a blowout win against Portland. Without Elton Brand, who was with his wife for the birth of his child, the Mavs won against the Toronto Raptors 109–104 with Chris Kaman starting for the first time and scoring 22, the same point amount that Mayo had. The Mavs fell, with Brand and Beaubois, to the New York Knicks who improved to a league-best 4–0 record. On the next night, the Mavs lost to Charlotte who defeated the Mavericks for the first time in 17 tries. The Mavs lost their first game at home and third straight game to the hands of the Minnesota Timberwolves. Against the winless Washington Wizards the Mavs took care of business and won by six, while putting up 40 points in the second quarter. Their next back-to-back started at the Indiana Pacers, who played without Danny Granger, but got the win in blowout fashion by 20. On the second night they took on the Cleveland Cavaliers and squeezed out a win by eight, 103–95. The Golden State Warriors came to town and defeated the Mavs after Overtime 105–101. Two days later, Jason Kidd and Tyson Chandler returned to Dallas with the New York Knicks. In a high scoring affair the Mavs closed it out and won by three, 114–111. The Lakers were next up to the Mavs on their home floor and got out there with a big win by 27. After a two-point loss against the Philadelphia 76ers the Mavs fell, for the first time this season, under .500. Without Collison the Mavericks failed on the second night of a back-to-back by losing to the Chicago Bulls. In the first game of Derek Fisher, which he started, the Mavs defeated the Detroit Pistons comfortably 92–77. When facing the Los Angeles Clippers, the Mavs got blown out by 22, the same number of turnovers they had for the game. On the next night, they won at the Phoenix Suns by three, after O. J. Mayo put them ahead late in the game. The Mavericks took on the Houston Rockets and it was a duel between James Harden and Mayo, who scored 39 and 40 points respectively. Mayo had the better on his side as the Mavs won by seven. Next up, the Mavs took care of the Sacramento Kings and blew them out 119–96. In the first game against ex-Maverick Jason Terry and his Boston Celtics the Mavs fell after double overtime. The Mavs moved to Canada to take on Toronto and got blown out badly. It also ended the streak of at least one three pointer in a game after 1,108 games, last time it happened was in 1999. On the next night they faced Minnesota and lost by eight after overtime, which moved their overtime record to 0–3. After being back on their home floor, the Mavs won against the 76ers, and split the season series against them. Without Fisher, Brand and Brandan Wright the Mavs lost by 15 to the Miami Heat. With Wright back, the Mavs fell to the Memphis Grizzlies by ten.Dirk Nowitzki returned against the San Antonio Spurs but the Mavs still lost by 38. The game at the Oklahoma City Thunder went into overtime, and the Mavs again fell short, this time by six. In Nowitzki's home debut, the Mavericks lost to the Denver Nuggets by 21. On the last game in 2012, Vince Carter made his starting debut for the season but could not prevent the Mavs from losing to the Spurs by 25. On New Year's Day the Mavs took on Washington and were able to win by nine, after being down by as much as 14 in the second quarter. In yet another overtime game, the Mavs fell to Miami by 10, which leads the Mavericks still winless in overtime games this season (0–6). Nowitzki made his first start in a game against the New Orleans Hornets, which marked the 15th different starting lineup this year for the Mavs. The Hornets meanwhile got out with a win in Overtime with Eric Gordon scoring eight points in the extra period, which marked the tenth consecutive loss for the Mavs in overtime. Back on the road, the Mavs lost to the Utah Jazz, which marked their 12th loss in the last 14 games. At LA, against the Clippers the Mavs failed to convert a 5-point lead going into the fourth quarter, to lose by six. Against the Kings, in the second night of a back-to-back, the Mavs won after overtime by five. The Mavs blew Memphis out back on their homecourt, by 21. Against Minnesota, who were without Kevin Love and coach Rick Adelman, the Mavs were able ton their third straight game, this time by 15. In another must-win game against Houston, the Mavs escaped with a five-point victory after being up by 11 in the fourth quarter. In yet another Overtime game against Oklahoma City, Kevin Durant scored 52 points (21 from the line) to help the Thunder win it. Mayo made a three to tie the game in regulation but Carter missed a chance to send it to double-obertime. At Orlando the Mavs had several double-digit leads before winning it by five in the end. Against the Sours, their third meeting, it looked like another 25+ loss but the Mavs were able to cut it down late, to lose by six.Bernard James made his first career-start against Phoenix, with both Brand and Kaman coming off the bench. The Mavs were able to win comfortabily by 15, in a game where Nowitzki moved past Allen Iverson in the all-time scoring list, now placed at 18th. In a rematch of Game 4 of the 2011 playoffs between Dallas and Portland, the TrailBlazers erased a 21-point deficit and won at the buzzer after a LaMarcus Aldridge shot. Without Nowitzki, against Golden State the Mavs lost another nailbiter, by three at the end. The Mavs were able to turn a fourth quarter in their favour and defeating the Suns for the third time this season. The Mavs lost their league-"best" ninth game by 20+ points against Oklahoma. Back home, the Mavs faced a must-win five-game homestand. They rallied back from 10+ points and won the game against Portland by 6 by just allowing 38 points in the second half after giving up 61 before the break. The Mavericks avoided to be swept by Golden State in the season series by beating them with 25. Against the Atlanta Hawks the Mavs lost by four, which shrunk their playoff hopes to a minimum. The last game before the all-star break was successful against Sacramento. Carter scored 17 points in the third quarter, surpassing Larry Bird on the all-time scoring leader list and made his 1,600 three pointer of his career. The Mavs started the post all-star season with a win against Orlando. At New Orleans, the Mavericks needed two late threes by Mike James and Carter to escape with a four-point victory. On a marquee matchup with playoff intense, the Mavs lost to the LA Lakers by four. On a back-2-back, the Mavs lost at home to Milwaukee and at Memphis, shrinking their playoff hopes to a minimum. After three straight losses the Mavericks won at Brooklyn by 8, after being up by 20 in the fourth quarter. At Houston, the Mavericks got blown out badly, 103–136. Three days later, in the second straight game against Houston, this time at home, the Mavericks squeezed out a win. At Detroit, the Mavericks were able to win by three, after being up by 15 in the third quarter. Their third straight win came at Minnesota, where they won easily by 23. At Milwaukee, the Mavs were able to extend their winning streak to four. At San Antonio, the M;avericks had a chance to win the game but Carter missed a three at the buzzer. Back home and having eight of their next nine games on their homefloor, the Mavs defeated Cleveland by ten, after being down by double digits midway through the third quarter. In their last season matchup against OKC, the Mavs lost another nailbiter, by six at the end. This game marked the return of Brand into the starting lineup. At Atlanta, the Mavs wrapped up their last road game against an eastern conference team with a victory, 127–113. When Brooklyn came to town, the Mavs were unable to contain a ten-point lead from the first quarter. They lost eventually by 17 at the end. When Jason Terry returned to Dalla, he received a standing ovation by his first check-in into the game. However, the Mavs defeated Boston by ten. In another pivotal matchup, against Utah this time, the Mavs were able to win by five in the end, with the fourth quarter being safely in their hands. The Mavericks stretched their winning streak to three after an overtime victory over the Clippers. With a chance to get back to .500, the Mavs got blown out by Indiana. The Mavs ended their homestand with a hard-fought victory against the Bulls. They were down double-digits multiple times but Nowitzki managed to carry them when he hit the go-ahead three-pointer with 2.9 seconds to go. At the Lakers the Mavericks were not able to hang with them and lost by 20. At Denver, where the Nuggets held a 33–3 record, the Mavericks felt short by one when Andre Iguodala made a game winning layup with 2.8 seconds to go. At Sacramento, the Mavericks scored 41 points in the second quarter en route to a victory. At Portland, the Mavericks got a victory which put them one game under .500. After a home loss to Phoenix, the Mavericks were eliminated for the playoffs for the first time since 2000. The Mavs won an overtime game against Denver 108–105. After winning New Orleans, the Mavs reached the .500 mark for the first time since December 12 (121 days) and were able to shave their beards with Nowitzki scoring the 25,000th point during his career. Against Memphis, the Mavericks lost by six. Their last game of the season, against New Orleans, was won, so the Mavs ended the season at .500 (41–41).