Cummins had been assisting Watson since the former Newcastle United player was appointed as manager on October 10th and will now take the position on a more permanent basis.
Cummins has been in charge of the club`s under-19 and reserve set-up for the past few seasons, helping the likes of Jon Mellish and Tom White break into the first-team picture as he guided the young Tynesiders to consecutive promotions.
As a player, he made over 100 appearances for Gateshead between 2011 and 2014, scoring 15 goals.
The Dublin-born 39-year-old was previously with Middlesbrough, Port Vale, for whom he appeared over 250 time, Darlington, Rotherham United and Grimsby Town and also represented the Republic of Ireland at under-20 and under-21 level.