Belfast (/ ˈbɛlfɑːst / or /-fæst /; from Irish: Béal Feirste, meaning "rivermouth of the sandbanks") is the capital and largest city of Northern Ireland, and the second largest on the island of Ireland. On the River Lagan, it had a population of 333,871 in 2015. Belfast was granted city status in 1888.

What is the capital and major population center of northern ireland? Let's have some stream of consciousness first.
To answer this question, we should know that: Belfast (/ ˈbɛlfɑːst / or /-fæst /; from Irish: Béal Feirste, meaning "rivermouth of the sandbanks") is the capital and largest city of Northern Ireland, and the second largest on the island of Ireland. So, the answer is Belfast.