The 35-year-old musician took to Instagram on Tuesday to share the exciting news, along with a snapshot of their adorable bundle of joy.
"I am a little late, but I celebrated #internationalwomensday the best way I know how," the proud dad captioned the black-and-white photo, which showed his wife cradling their baby boy. "Marveling at the superpower women are uniquely gifted... as well as freaking out over the fact that I am now responsible to help raise another person."
Hanson also revealed the name of his newborn son, whom the couple welcomed on Sunday -- Quincy Joseph Thoreau Hanson.
The cute couple are already parents to daughters Junia, 10, and Mary, 4, and sons John, 12, and George, 7.
The Hanson drummer and his wife started dating in 2001 and tied the knot in June 2006.
The couple's exciting news news comes just a few months after the musician's big brother and bandmate, Taylor Hanson, welcomed his seventh child, a baby girl named Maybellene Alma Joy, with wife Natalie.
Congrats to the happy couple on the new addition to their family!