Bosses will only be allowed to contact employees in "exceptional circumstances", the Süddeutsche Zeitung newspaper reported on Friday, after Labour minister Ursula von der Leyen signed off the new rules.
Employees will also not be penalized for turning off their mobile phones or failing to return messages while off duty.
Out-of-hours contact from managers is only allowed when something is so urgent it can no wait until the next working day.
Von der Leyen signed off the new rules to try to stop employees taking work home with them, something which has become easier to do with laptops, emails and smart phones.
The ministry said they were the first public body in Germany to introduce such rules which were agreed following long discussions between the staff council and management.
Von der Leyen told the Süddeutsche Zeitung: "The process to introduce rules to protect the well-being [of the staff] was as difficult as it was rewarding."
She added that it was very important for employees, who could now technically be reached anywhere, to know when they should be contactable - and when they could switch off. "They now have this clarity in black and white," she said.
The minister first called for "clear rules" on work mobile phones a year ago. She said it was in the interest of employers that their staff could switch off from their work to avoid burnout.
The Labour Ministry has followed in the footsteps of Volkswagen in setting out strict rules on when managers can contact staff out of work hours.
At Volkswagen, which introduced their rules in 2011, emails can not be sent 30 minutes after a shift has finished.