New Democratic Party leadership elections, more commonly known as 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 New Democratic Party convention, since 1961, was a leadership convention. However, in practice, contested elections were held only when there was a declared leadership race. The earliest example of an incumbent leader being challenged from the convention floor happened in 1973 when Douglas Campbell unsuccessfully opposed David Lewis' leadership.^[1] In 2001, Socialist Caucus member Marcel Hatch challenged Alexa McDonough from the floor of the convention; however, McDonough easily retained the leadership in the resulting vote.^[2]

When the NDP was created by the merger of the Co-operative Commonwealth Federation (CCF) and the Canadian Labour Congress (CLC), trade unions were allowed to directly affiliate to the party, and a system was unofficially 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.^[3] This was also the case at leadership conventions, giving the labour movement a significant say in determining the party's leadership. Under the current system, each biennial federal convention includes a vote at which the delegates decide whether a leadership convention should be held.^[3] Then-leader Thomas Mulcair lost such a vote at the 2016 convention, resulting in the 2017 leadership election being called.^[4]

In practice, all three CCF leaders had been chosen by their parliamentary caucus and then elected unanimously at a subsequent national convention.

1961 leadership convention results

Held in Ottawa, Ontario on August 3, 1961.^[5]

First Ballot

Candidate		Delegate Support	Percentage
	DOUGLAS, Thomas Clement (Tommy)	1,391	78.5%
	ARGUE, Hazen Robert	380	21.5%
Total		1,771	100%

1971 leadership convention results

Held in Ottawa, Ontario on April 24, 1971.

Delegate Support by Ballot

Candidate		1st ballot		2nd ballot		3rd ballot		4th ballot
		Votes cast	%	Votes cast	%	Votes cast	%	Votes cast	%
	LEWIS, David	661	38.9%	715	42.5%	742	44.1%	1,046	63.1%
	LAXER, James	378	22.3%	407	24.1%	508	30.2%	612	36.9%
	HARNEY, John Paul	299	17.6%	347	20.5%	431	25.6%	Eliminated
	BROADBENT, John Edward (Ed)	236	13.9%	223	13.1%	Eliminated
	HOWARD, Frank	124	7.3%	Eliminated
Total		1,698	100.0%	1,692	100.0%	1,681	100.0%	1,658	100.0%

1973 leadership challenge results

Held in Vancouver, British Columbia on Friday, July 20, 1973.^[1]

First Ballot

Candidate		Delegate Support	Percentage
	LEWIS, David	719	90.4%
	CAMPBELL, Douglas Kay	76	9.6%
Total		795	100%

1975 leadership convention results

Held in Winnipeg, Manitoba on July 7, 1975.

Delegate Support by Ballot

Candidate		1st ballot		2nd ballot		3rd ballot		4th ballot
		Votes cast	%	Votes cast	%	Votes cast	%	Votes cast	%
	BROADBENT, John Edward (Ed)	536	33.1%	586	36.1%	694	43.4%	984	61.5%
	BROWN, Rosemary	413	23.5%	397	24.5%	494	30.9%	658	41.1%
	NYSTROM, Lorne Edmund	345	21.3%	342	21.1%	413	25.8%	Eliminated
	HARNEY, John Paul	313	19.4%	299	18.4%	Eliminated
	CAMPBELL, Douglas Kay	11	0.6%	Eliminated
Total		1,618	100.0%	1,624	100.0%	1,601	100.0%	1,642	100.0%

1989 leadership convention results

Held in Winnipeg, Manitoba on December 2, 1989.

Delegate Support by Ballot

Candidate		1st ballot		2nd ballot		3rd ballot		4th ballot
		Votes cast	%	Votes cast	%	Votes cast	%	Votes cast	%
	MCLAUGHLIN, Audrey Marlene	646	26.9%	829	34.3%	1,072	44.4%	1,316	55.1%
	BARRETT, David (Dave)	566	23.6%	780	32.3%	947	39.3%	1,072	44.9%
	LANGDON, Steven W.	351	14.6%	519	21.5%	393	16.3%	Eliminated
	DE JONG, Simon Leendert	315	13.1%	289	12.0%	Endorsed McLaughlin
	MCCURDY, Howard Douglas	256	10.7%	Withdrew
	WADDELL, Ian Gardiner	213	8.9%	Withdrew
	LAGASSÉ, Roger	53	2.2%	Eliminated
Total		2,400	100.0%	2,417	100.0%	2,412	100.0%	2,388	100.0%

1995 leadership convention results

Held in Ottawa, Ontario on October 14, 1995.

Support by Round

Candidate		Primaries	1st ballot
			Votes cast	%
	NYSTROM, Lorne Edmund	44.69%	545	31.5%
	ROBINSON, Svend	32.06%	655	37.8%
	MCDONOUGH, Alexa Ann	18.47%	566	32.6%
	HARDIN, Herschel	12.8%	Did not endorse
Total		100.0%	1,735	100.0%

The NDP held a series of regional and labour "caucus votes" prior to the national convention. A fourth candidate, Herschel Hardin, participated in the regional caucuses but did not win sufficient delegate support to qualify for the convention. These "primaries" were OMOV.

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, as they were expected to, thus he withdrew and McDonough was declared the winner.

2001 leadership challenge results

Held in Winnipeg, Manitoba on Sunday, November 25, 2001.

Marcel Hatch, a leader of the NDP's Socialist Caucus, stood for leader as a challenge to Alexa McDonough's leadership.^[6]

First Ballot

Candidate		Delegate Support	Percentage
	MCDONOUGH, Alexa Ann	645	84.31%
	HATCH, Marcel	120	15.69%
Total		765	100%

There were 42 spoiled ballots. If these are factored in McDonough's level of support was 78% overall.^[7]

2003 leadership election results

Held in Toronto, Ontario on January 25, 2003.

First Ballot

Candidate		Votes (Adjusted)	Percentage
	LAYTON, John Gilbert (Jack)	31,150	53.5%
	BLAIKIE, William Alexander (Bill)	14,365	24.7%
	NYSTROM, Lorne Edmund	5,397	9.3%
	COMARTIN, Joseph John (Joe)	4,490	7.7%
	DUCASSE, Pierre	2,155	3.7%
	MESLO, Beverley (Bev)	645	1.1%
Total		58,202	100%

For this election, the NDP instituted a modified one member one vote system. Votes by labour delegates accounted for 25% of the total result, while votes cast by party members accounted for 75%. The carve out for labour was eliminated prior to the 2012 election.

2012 leadership election

The leadership convention was held at the Metro Toronto Convention Centre on March 24, 2012.^[8][9] There were 128,351 eligible voters, most voting from home and not delegates at the convention.^[10]

The party chose Thomas Mulcair as their new leader following the death of Jack Layton on August 22, 2011. A One member, one vote process was used.^[11]

  = Eliminated from next round

  = Withdrew nomination

  = Winner

Support by Ballot

Candidate		1st ballot		2nd ballot		3rd ballot		4th ballot
		Votes cast	%	Votes cast	%	Votes cast	%	Votes cast	%
	MULCAIR, Thomas Joseph (Tom)	19,728	30.3%	23,902	38.3%	27,488	43.8%	33,881	57.2%
	TOPP, Brian	13,915	21.4%	15,624	25.0%	19,822	31.6%	25,329	42.8%
	CULLEN, Nathan	10,671	16.4%	12,449	19.9%	15,426	24.6%	Did not endorse
	NASH, Peggy A.	8,353	12.8%	10,519	16.8%	Did not endorse
	DEWAR, Paul W.	4,883	7.5%	Did not endorse
	SINGH, Jarnail Martin John	3,821	5.9%	Endorsed Mulcair
	ASHTON, Niki Christina	3,737	5.7%	Did not endorse
	SAGANASH, Diom Roméo	Endorsed Mulcair
	CHISHOLM, Robert Lawrence	Endorsed Mulcair
Total		65,108	100.0%	62,494	100.0%	62,736	100.0%	59,210	100.0%

2017 leadership election

Voting was held between September 18 to October 1, 2017. The results were announced on October 1 in Toronto, Ontario at the Westin Harbour Castle.

First Ballot

Candidate		Votes	Percentage
	SINGH, Jagmeet Jimmy Dhaliwal	35,266	53.8%
	ANGUS, Charles Joseph (Charlie)	12,705	19.4%
	ASHTON, Niki Christina	11,374	17.4%
	CARON, Guy	6,164	9.4%
Total		65,782	100%

• Spoiled ballots: 101
• Abstentions: 172
• Turnout: 52.8% (1.9pp)^[12]