Charlie Broadway, 23, has been held on suspicion of murder and attempted murder following the double shooting at the Chubbards Cross caravan park, near Ilton, north of Ilminster, Somerset, shortly before 8pm on Thursday.
A man in his 50s died at the scene and a second man - in his 20s - received "non life-threatening" injuries.
Avon and Somerset Police said Broadway handed himself into police at a custody centre in Somerset this afternoon.
After revealing the breakthrough in the investigation, police said they wanted to speak to two other people over the incident.
Detective Superintendent Andy Bevan said: "I would like to thank each and every member of the public who have assisted us with this investigation.
"I would also like to extend my thanks to the media who publicised our appeal far and wide.
"As part of this on-going inquiry we are now also keen to speak to John Broadway, 37, and Donna Broadway, 26, who have yet to come forward.
"John is described as white, with dark brown hair, brown eyes and a thin build.
"Neither are considered to pose any risk to the public but we would urge the pair to contact us directly.
"Anyone with information as to the whereabouts of these two should call us now on 999 and quote log number 1051 of May 5."
Later, police said Donna Broadway was Charlie Broadway's wife and John Broadway was his elder brother.
Tributes have been paid on social media to the man who died, who has been named locally as Wilf Isaacs.
Teresa Winter posted photographs of Mr Isaacs on Facebook and wrote: "Rip uncle wilfie love you all the world best man in somerset! Xxxx"
Mr Isaacs' son Barry shared a link to a news report on the hunt for Broadway.
Natasha Woolacott wrote: "So so sooo sorry to hear it Barry, he was such a lovely man, thinking of you & family xxxxx."
Deb Hull added: "Such tragic news, so sorry Barry, Pammy, Wilfie, Tabi and family, he was a good man, my thoughts and prayers are with you all xxx."