Seattle police spokeswoman Renee Witt said officers went to the scene, a home in the 8900 block of 31st Avenue NW, shortly after 1 a.m. after receiving a report of shots fired.
As the SWAT team surrounded the home, they heard two shots from inside the residence.
Hostage negotiators eventually made phone contact with the suspect, who voluntarily left the home. He was taken into custody without incident.
The handgun was found inside the home and two fresh bullet holes were found in the basement apartment, Witt said.
A second handgun and six rifles were also taken into custody for safekeeping. The man was taken to the hospital on 72-hour involuntary commitment.