The former Privett Park assistant manager – who left the club in January – takes the hot seat at Borough after Alex Pike was sacked last week.
Catlin got the job ahead of Graham Rix, Adrian Whitbread and current assistant Danny Thompson, who had been holding the reins.
Chairman Ian Sellstrom is confident he has appointed the right man during a difficult period at Privett Park.
He said: ‘Mick ticked all the boxes of the criteria we were looking for.
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‘He knows the club, the local area and understands the ethos and importance of community for clubs like ours.
‘His knowledge of local talent will be invaluable and he will be able to shop around albeit with a limited budget.
‘It won’t be easy and is likely to be a bit of a roller coaster ride for all of us.
‘With this appointment I feel the club will be in the right hands for the next few years.
‘We have agreed some milestones to try and get us where we need to be.
‘The first target is to stay in the Southern League premier division.
‘There are further changes planned for the club to try and put it on the right footing for the future.’
Borough received a further blow off the field yesterday when chief executive officer Mark Adams resigned after just nine weeks in the role.
Adams felt he didn’t have the full co-operation of the board.
In his statement, however, he admitted Sellstrom had acted with complete integrity throughout.