The popstar's wife Barrett gave birth to daughter Kira Katherine McIntyre on Tuesday afternoon, according to a message on the star's Twitter account.
The singer told followers that the new arrival weighed 7lbs 3oz and measured 21in. "A beautiful baby girl with great timing and gorgeous hair," he added.
The couple are already parents to sons Griffin, 3, and 1-year-old Rhys.
McIntyre's bandmate Jordan Knight was among the people who offered their congratulations over the social networking site, writing: "Can't believe my kid brother now has more kids than me!!! Congrats @Joeymcintyre!!!"
New Kids On The Block are currently on a summer tour alongside the Backstreet Boys. The two bands have also released a joint album which contains the new song 'Don't Turn Out The Lights'.
Listen to the New Kids On The Block and Backstreet Boys song 'Don't Turn Out The Lights' below: