The man shot at a solicitors office in Devizies, Wiltshire has been named locally as James Ward, a principal partner at the firm Morris, Goddard and Ward.
The 58-year-old father-of-three remains in a "very serious condition" in hospital after a man walked into his office and fired a shotgun at his head. His family are by his bedside.
Ward, who specialises in family law, was described as a "lovely man" by one of his neighbours, the Guardian reported.
"I can't think why anybody would have done this," the man added.
Emergency services rushed to the incident at St John's Street, in Devizes, Wiltshire at 2.55pm on Monday. According to locals, a loud noise like a car backfiring was heard in the street.
A Wiltshire Police spokeswoman said a 62-year-old man was arrested in connection with the incident about 40 minutes later.
"A male walked into the offices of David Nolder & Co. armed with a weapon and shot a male," the spokeswoman said.
"The offender drove off in a car but was arrested at approximately 3.35pm without a struggle by armed officers in Rowde.
"We recovered a weapon which we believe was used in the incident.
"The victim has sustained what are believed to be life threatening injuries and was airlifted to Frenchay hospital for treatment."
The arrested man is now in custody at Melksham Police Station.
Claire Perry, the Conservative MP for Devizes, wrote of her shock at the shooting on Twitter.
"All thoughts and prayers with the victim of the tragic shooting today in Devizes, and his family," she wrote this evening.
"What an awful, shocking thing to happen."
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