New Hampshire Attorney General John Formella and Nashua Police Chief Kevin Rourke said Robert Steven DeCesare, 59, died after he was shot at the Sky Meadow Country Club in Nashua.
Authorities said the suspect, Hunter Nadeau, age 23, was detained at the scene and later charged with one count of second-degree murder for knowingly shooting DeCesare.
"Additional charges likely will be brought, including for the additional shooting victims," Formella and Rourke said in a statement.
They said they expected Nadeau to be arraigned at the Ninth Circuit Court in Nashua on Monday.
Authorities had initially thought there could be two shooters but later said there was only one.
Investigators were still working to determine a motive, New Hampshire Senior Assistant Attorney General Peter Hinckley said.
Authorities said there was no known connection between Nadeau and DeCesare.
Information on the wounded victims' conditions was not immediately available.
US representative Maggie Goodlander said in a statement she was "closely monitoring the tragic reports of a shooting tonight at Sky Meadow Country Club in Nashua" and that her heart was with the victims, their families and the community.
Tom Bartelson of Pepperell, Massachusetts, who was at the country club, described a chaotic scene that unfolded near his nephew's wedding.
He said he heard the shooter say "the children are safe" and "free Palestine" and appeared to be targeting someone.
"Getting together for a dance for the bride and groom and then all chaos went off," he said.
"We heard about six shots and everybody ducked for cover and next thing you know, we're rushed into safe spots."
He said some people dropped to the ground and attempted to get away from the scene. There was a lot of panic, he said.
"We were trying to keep family members safe," he said.
The mother of DeCesare, the man who was killed, had earlier described not being able to find her son after he was shot.
"He went down. My daughter-in-law and granddaughter escaped ... They saw my son go down and they saw blood," Evie O'Rourke of Salem, New Hampshire, said.
Nashua Mayor Jim Donchess said he had faith in police to "get to the bottom of this and bring the perpetrator to justice".
"I think the message is for every community out there is that no matter how unlikely it seems, it can happen where you live," he said.
Nashua is about 70km northwest of Boston, just across the Massachusetts border.
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