Matt McCarten is a New Zealand political organiser. He has been involved with several leftist or centre-left political parties, and is also active in the trade union movement.

McCarten was originally a member of the Labour Party, but grew dissatisfied with the party's direction under Minister of Finance Roger Douglas. Douglas was a strong promoter of free market economics and deregulation, which McCarten and others saw as a betrayal of Labour's roots. Eventually, one of Labour's MPs, Jim Anderton, broke away to found NewLabour, and McCarten became the president of the new organisation. NewLabour later joined with several other parties to form the Alliance — McCarten became president of this new party as well.

After the 1999 elections, the Alliance became the junior partner in a coalition government with Labour (which had now moved away from its program of economic reforms). However, some members of the Alliance, including McCarten, felt that too many concessions had been made to the more centrist Labour, and that the Alliance was abandoning its left-wing principles. Eventually, a rift developed between McCarten (serving as the Alliance's organisational leader) and Jim Anderton (serving as its political leader) — the party's governing Council backed McCarten, but most of its MPs backed Anderton. According to some, there was also a strong clash of personalities — both McCarten and Anderton have been accused by opponents of being controlling and autocratic. After a long and bitter dispute, Anderton and his supporters left the Alliance to found the Progressive Party, leaving McCarten's faction in control of the Alliance.

The Alliance, now led politically by Laila Harré, suffered heavily in the 2002 elections, losing all representation in Parliament. The following year, McCarten himself assumed the political leadership from Harré. He was compelled to resign this position in November 2004, however, after becoming increasingly involved with campaign work for the new Maori Party. McCarten believed that the Alliance and the Maori Party were compatible, and that they should not regard each other as rivals, but this view was not shared by the members of either group. McCarten chose to leave the Alliance to focus on the Maori Party.

In early 2005, however, McCarten ended his association with the Maori Party as well. According to media reports, McCarten is in the process of establishing a new left-wing party for the "working poor", and was asked by the leadership of the Maori Party to choose between his two ventures. It is unclear whether McCarten will be able to launch and register this new party (possibly to be called the Aotearoa New Zealand Party) by the 2005 elections.