The scheme is called Project Warhol and is inspired by similar initiatives from major Silicon Valley brands.
To receive the investment and support, employees must demonstrate that the ideas and projects will benefit their agency and Next 15.
Ideas will be submitted to an investment panel, including Next 15 board members and representatives of the agencies. Staffers whose concepts are approved with the panel will be paired with a business mentor to develop a comprehensive business plan.
"Project Warhol will help drive innovation within the Next 15 group, supporting budding entrepreneurs," said Tim Dyson, CEO of Next 15.
"Along with helping employees to work on projects they’re personally passionate about, the fund has the potential to help Next 15 as a whole, providing innovative investment opportunities and the chance to help create start-ups with a world-class team of people.
"It’s a win-win situation, with employees able to enjoy the support and resources necessary to develop their ideas, and bring some brilliant new concepts, products and businesses keeping Next 15 agencies at the forefront of marketing technology innovation."
Earlier this month, Next 15 reported a 50 per cent rise in pre-tax profit to £24.2m ($30.1m) in the year to 31 January, boosted by growth in the US and higher margins elsewhere, and aided by acquisitions and favourable exchange rates.