NDP leadership conventions are the process by which the Canadian New Democratic Party elects its leader.

Before 2003, when a modified one member, one vote (OMOV) system was adopted, every biennial convention of the Cooperative Commonwealth Federation (CCF) and its successor, the New Democratic Party, was a leadership convention.

However, in practice, contested elections were only held when there was a declared leadership race. In 2001, a rare exception to this occurred when Socialist Caucus member Marcel Hatch challenged Alexa McDonough from the floor of the convention; however, McDonough easily retained the leadership in the resulting vote. It also seems that in 1973 Douglas Campbell unsuccessfully challenged David Lewis' leadership.

CCF leaders J.S. Woodsworth in 1933, M.J. Coldwell in 1942 and Hazen Argue in 1960 were all elected by acclamation.

In 1961, the CCF and the Canadian Labour Congress joined to form the New Democratic Party . Trade unions were allowed to directly affiliate to the party, and a system was arranged so that up to one-third of all delegates to NDP conventions were selected by labour and the other two-thirds by NDP riding associations. This was also the case at leadership conventions, giving the labour movement a significant say in determining the party's leadership.

1961 NDP Leadership Convention Results

Held in Ottawa, Ontario on August 3, 1961.

First Ballot
DOUGLAS, Thomas Clement (Tommy) 1391
ARGUE, Hazen Robert 380
Total Votes Cast 1771

1971 NDP Leadership Convention Results

Held in Ottawa, Ontario on April 24, 1971.

First Ballot
LEWIS, David 661
LAXER, James 378
HARNEY, John Paul 299
BROADBENT, John Edward 236
HOWARD, Frank 124
Total of Votes 1698

Second Ballot
LEWIS, David 715
LAXER, James 407
HARNEY, John Paul 347
BROADBENT, John Edward 223
Total Votes Cast 1692

Third Ballot
LEWIS, David 742
LAXER, James 508
HARNEY, John Paul 431
Total Votes Cast 1681

Fourth Ballot
LEWIS, David 1046
LAXER, James 612
Total Votes Cast 1658

1975 NDP Leadership Convention Results

Held in Winnipeg, Manitoba on July 7, 1975.

First Ballot
BROADBENT, John Edward 536
BROWN, Rosemary 413
NYSTROM, Lorne Edmund 345
HARNEY, John Paul 313
CAMPBELL, Douglas 11
Total Votes Cast 1618

Second Ballot
BROADBENT, John Edward 586
BROWN, Rosemary 397
NYSTROM, Lorne Edmund 342
HARNEY, John Paul 299
Total Votes Cast 1624

Third Ballot
BROADBENT, John Edward 694
BROWN, Rosemary 494
NYSTROM, Lorne Edmund 413
Total Votes Cast 1601

Fourth Ballot
BROADBENT, John Edward 984
BROWN, Rosemary 658
Total Votes Cast 1642

1989 NDP Leadership Convention Results

Held in Winnipeg, Manitoba on December 2, 1989.

First Ballot
MCLAUGHLIN, Audrey Marlene 646
BARRETT, David 566
LANGDON, Steven W. 351
DE JONG, Simon Leendert 315
MCCURDY, Howard Douglas 256
WADDELL, Ian Gardiner 213
LAGASSE, Roger 53
Total Votes Cast 2400

Second Ballot
MCLAUGHLIN, Audrey Marlene 829
BARRETT, David 780
LANGDON, Steven W. 519
DE JONG, Simon Leendert 289
Total Votes Cast 2417

Third Ballot
MCLAUGHLIN, Audrey Marlene 1072
BARRETT, David 947
LANGDON, Steven W. 393
Total Votes Cast 2412

Fourth Ballot
MCLAUGHLIN, Audrey Marlene 1316
BARRETT, David 1072
Total Votes Cast 2388

1995 NDP Leadership Convention Results

Held in Ottawa, Ontario on October 14, 1995.

First Ballot
ROBINSON, Svend Johannes 655
MCDONOUGH, Alexa 566
NYSTROM, Lorne Edmund 345
Total Votes Cast 1735

As the last place finisher on the first ballot, Nystrom was dropped. However, Robinson determined that he could not win on the second ballot if Nystrom's supporters moved to McDonough, thus he withdrew and McDonough was declared the winner.

(Note: During this leadership contest, the NDP held a series of regional "caucus votes" prior to the national convention. A fourth candidate, Herschel Hardin, also participated in the regional caucuses, but did not win sufficient delegate support to qualify for the convention.)

2001 NDP Leadership Challenge Results

Held in Winnipeg, Manitoba on December 2, 1989.

First Ballot
MCDONOUGH, Alexa 645
HATCH, Marcel 120
Total Votes Cast 765

2003 NDP Leadership Election Results

Held in Toronto, Ontario on January 25, 2003.

First Ballot
LAYTON, Jack 31150 (54%)
BLAIKIE, William Alexander (Bill) 14365 (24.7%)
NYSTROM, Lorne Edmund 5397 (9.3%)
COMARTIN, Joe 4490 (7.7%)
DUCASSE, Pierre 2155 (3.7%)
MESLO, Bev 645 (1.1%)
Total Votes 58202

Starting with the 2003 leadership election the NDP instituted a modified one member one vote where the vote is calculated so that ballots cast by labour delegates have 25% weight in the total result while votes cast by party members have 75%.