Brent sets out on a self-funded tour, but has to "cash in a couple of pensions because the session musicians are costing him more than he's getting in ticket sales".
Described by the BBC as "a philosopher to rival Descartes, a musician to rival Texas and a dancer to rival MC Hammer", Brent became an iconic character.
Shown in more than 100 countries and remade in eight, The Office is the most successful British comedy ever.
Rumours of a movie first surfaced last year but only now have more details been released and the green light given.
Gervaish has performed several UK gigs in character as part of his band Foregone Conclusion and launched a YouTube channel featuring 'Learn Guitar' videos.
He is nominated for the Lead Actor in Comedy accolade at this year's Emmy Awards, alongside Shameless' William H Macy and The Big Bang Theory's Jim Parsons.