A total of 138 candidates from across the political spectrum are running in the 18 constituencies.
Polling stations opened at 7 am and will close at 10 pm tonight.
Counting will take place overnight in eight different centres and the first results in Northern Ireland are expected around 1 am on Friday morning.
The main Belfast count is taking place at the Kings Hall.
Constituencies of interest will be Fermanagh and South Tyrone where Sinn Fein’s Michelle Gildernew holds a majority of four votes.
The DUP’s Gavin Robinson is the bookies favourite to regain east Belfast from the Alliance’s Naomi Long.
And south Belfast is also a seat of interest where the SDLP’s Alasdair McDonnell is fighting to stave off advances from the DUP’s Jonathan Bell and former Sinn Fein Belfast Lord Mayor Mairtin O’Muilleoir.