Mr Gargan, 48, was suspended following allegations of data protection breaches and inappropriate behaviour with women.
A panel found him guilty of misconduct - but cleared him of gross misconduct.
Avon and Somerset Police and Crime Commissioner Sue Mountstevens said Mr Gargan's suspension would be lifted and a phased return to work prepared.
In a statement, Mr Gargan said he accepted the panel's findings and apologised that his actions had "fallen below the standards expected of a chief constable".
"I am pleased that the more serious gross misconduct allegations were found not to be proven, including any allegation of inappropriate advances towards female colleagues," he said.
"I am relieved and very pleased that my suspension is at an end."
Mr Gargan, who has been suspended on full pay since May 2014, faced 10 charges of gross misconduct and three charges of misconduct. The PCC said he was found guilty of eight charges at a level of misconduct.
There was insufficient evidence to bring criminal charges over the alleged data protection breaches.
The chair of the Avon and Somerset Police Federation, Kevin Phillips, said there would be "an awful lot of concerned police officers".
Mr Phillips added: "The people who have stood up and said something should be protected and can't be victimised.
"I have no doubt whatsoever that they will have concerns and they will be looking over their shoulders."
Panel chair Dorian Lovell-Pank QC will now write a report of its findings and will recommend any sanctions Mr Gargan should face under police regulations.
The panel met behind closed doors even though Ms Mountstevens wanted the proceedings held in public.
Avon and Somerset Chief Constable Nick Gargan has been found guilty of eight charges of misconduct but will be allowed to return to work.