Normally taking between 47%-51% of the vote. The main community providing this vote is the Protestant community, and descendants of the Scottish and English settlers to Ulster. This group contains some Catholics. Consider that only 4% of Protestants identify as "Irish" while 13% of Catholics identify as "British". Around one third of both groups simply identify as "Northern Irish".
5 parties, the DUP, UUP, TUV, UKIP, and the PUP. All are officially unionist. There are other "officially" unionist parties, such as NI Conservatives, but their vote total and impact is so minor, I've counted them in with the "Other" parties.
These parties have taken 329,709 votes combined in the last election,
A cautionary note as well, I will only be looking at parties that still exist, and as such, historic Unionist parties of importance will not be examined here.
Democratic Unionist Party
The DUP is currently the largest Unionist party in Northern Ireland. One can not look at the party without looking at it's larger-than-life founder, Ian Paisley.
Paisley was originally a member of the UUP. During that time he set up Ulster Protestant Action, a group dedicated to defending against anticipated IRA attacks. They would march down the street rounding up 'suspects'. This group would later grow into the Protestant Unionist Party which ran for 4 years. This party was folded into the DUP upon the latter's founding in 1971.
The main priority of the DUP during it's early decades would be to oppose power sharing, a stance it more or less maintained until 2007 when it received certain concessions from Sinn Fein and the PIRA about weapons and policing. Ian Paisley would then go on to become First Minister.
The DUP's political stances can be defined as generally right-wing and conservative, and many party members hold socially conservative views. One thing dividing the DUP and UUP is demographics. While both parties find support all across the Protestant community, DUP members are more likely to be Ulster Scots and Presbyterians,
Following Paisley's resignation as leader (he was 80 at the time) Peter Robinson took over. After being forced out by numerous scandals, Arlene Foster became leader. Foster now faces her own scandal in the RHI.
In the most recent election, the DUP took 61.4% of the Unionist vote, a level at which the party has remained for nearly a decade.
Ulster Unionist Party
The UUP can trace it's history back to the 1880's with the Irish Loyal and Patriotic Union; which attempted to oppose the Irish Parliamentary Party in the 1885 election. The ILPU backed Conservative candidates and encouraged Liberals to vote Conservative to stop the IP. A group of Liberal Unionists would alter break off from the Liberals and effectively join the Conservatives in Ireland as the Unionist Party. In 1892 the Irish Unionist Party managed to win most of the seats that would later be within Northern Ireland. In 1921 with the creation of Northern Ireland the party adopted it's current name.
For the first 4 decades, the UUP would remain unrecognizable compared to the party we know today. Lead by aristocrats and with deep ties to the Orange Order, the party did not even allow Catholic members for some time.
The modern party started to take shape under Terrance O'Neill, the Prime Minister of Northern Ireland in the 60's. He began to implement reforms to allow for better participation of Catholics within Northern Ireland. This would split the party, and over time, those who opposed O'Neill and his pro-reform successors such as Brian Faulkner, and David Trimble. Trimble would be elected leader in 1995, following a long period of minimalist UUP policies for fear of dividing the party.
Trimble originally appeared as a hardliner, would would quickly become the first UUP leader in decades to meet with the Irish Prime Minister, and the first Unionist leader to negotiate with Sinn Fein. Trimble made the UUP what it effectively is today, a Unionist party willing to negotiate. Despite attempts to join forces with the PUP, and the Conservatives, the UUP remains an independent political party.
After a sharp decline which included a period where the UUP had no Members of Parliament in Westminster, the UUP perhaps has the most to gain from the DUP's scandals. The UUP and DUP are the main combatants over protestant voters, despite the fact that UUP membership leans more towards Anglicans.
In 2016, the UUP Took 26.5% of the Unionist vote.
Traditional Unionist Party
The TUV was founded by Jim Allister, a former member of the DUP. In 2007 when the DUP agreed to sit in Stormont in government with Sinn Fein, Allister, at the time a member of the European Parliament, quit the party.
the TUV is opposed to the current executive, and wants a return to majority rule, where a party only needs to cobble together a coalition of 50%+1 of all seats in the assembly to govern, regardless to weather all those seats be Unionist or Nationalist. The TUV calls for a barrier of 60% of the entire assembly to approve of a new government, with that dropping to 50% over time.
the TUV is avowedly right-wing, especially on social issues. It's 2016 platform explicitly spelled out it's opposition to same sex marriage, and abortion.
The TUV managed 7.2% of the Unionist vote in 2016.
United Kingdom Independence Party
UKIP was founded in Britain by Brits. The party has only recently taken an interest in Northern Ireland. In 2014, UKIP took 4% of the vote in European elections in NI.
The party's first local success happened in 2011, when Henry Reilly, who defected from the UUP, joined UKIP. Reilly was a local councillor from Newry and the Mournes. In 2011 he was re-elected for his DEA, topping the ballot with 27.7% of the vote. The largest success was when David McNarry defected from the UUP giving the party it's first MLA. McNarry did not run for re-election in 2016, however, and UKIP failed to take any seats.
In 2014, Reilly was re-elected to the new and larger Newry, Mourne and Down council from The Mournes, again topping the poll. Reilly was then unexpectedly suspended from UKIP without explanation. He joined the TUV until November of 2016, when he joined an unnamed charity, and amicably parted with the TUV.
In the most recent assembly election UKIP has taken 3.1% of the Unionist vote.
Progressive Unionist Party
Associated with a loyalist paramilitary, the PUP was officially founded in 1979, the party was focused around Hugh Smyth. Smyth was first elected to Belfast city council in 1973 representing the Shankill area. In 1975, Smyth managed election to the advisory assembly at Stormont, which quickly collapsed. Smyth would continue to be re-elected for the Belfast council, but victories for other PUP members would be few and far between.
The party's success came after the 1994 cease fire. Smyth would serve a year as Lord Mayor of Belfast; a post with mayoral powers that is rotated between parties once every calendar year. In 1997, the PUP would reach 9.2% in the local Belfast election, and elect 3 members to council. The party also held sets in the assembly until the 2011 election.
Smyth would resign as leader in 2002 to make way for a younger generation. The current leader is Billy Hutchinson. Hutchinson considers himself an atheist and has declared support for socialism. It is important to note the PUP is a left-wing party, something unique among Unionist parties. All 3 parties that cater to Nationalist voters are openly left-wing, while the 4 Unionist parties listed above are openly right-wing. The PUP is the only exception to that general rule, being a left-wing but unionist party.
Currently, the party holds 0 assembly seats, but has 3 seats on the Belfast city council, and one in the Causeway Coast and Glens.
In 2016 the party took 1.8% of the Unionist vote.