EngineeringUK and the British Science Association are holding a closed pitch for the £180,000 brief, which is to promote next year's event at NEC Birmingham in March.
EngineeringUK is an independent not-for-profit organisation that supports the contribution of engineers, engineering and technology to society, while the BSA is a charity promoting access to science for everyone.
The brief also covers the National Science + Engineering competition, which takes place during the fair. The competition is co-ordinated by the BSA and funded by the Department for Business, Innovation and Skills.
Targets for comms work include young people aged seven to 19 and their influencers, such as parents, teachers and careers professionals.
Additional stakeholder engagement will include work with civil servants, MPs and ministers in Government and opposition.
PR for the Big Bang Fair in 2013 was handled by Consolidated PR, with 65,000 attending this year's four-day show in March.
The fair is supported by the Department for Business, Innovation and Skills as part of a wider effort to boost numbers of science, technology, engineering and maths (STEM) graduates.
Pressure on the Government to support the subjects was increased by a report released in March by the Social Market Foundation, which claimed the number of STEM graduates needed to increase by half just to maintain science-related industries at their current size.
One well-placed source called the drive to increase STEM skills 'vital' to government efforts to drive the economy: 'It's not just about graduates, but about increasing apprenticeships and upping diversity.
'To get ministers onside, however, the selected agency would need to engage with young people in a sector where that hasn't been done as well as it could have.'