The programme will help start-ups develop security software into fully fledged commercial products and connect them with tech experts across GCHQ itself and the National Cyber Security Centre.
The spooks originally selected seven vendors for the first phase of the scheme in January, but has now extended the programme to nine months and is encouraging another wave of start-ups to apply.
The first seven vendors have raised more than £2.7 million in investment, the government said, and have won deals with tech giants including Cisco.
Matt Hancock, minister for digital, said: “We are working hard to make Britain the best place to start and grow a digital business, and the safest place to be online.
“The GCHQ Cyber Accelerator is a vital part of this work and has already helped some of the most innovative cyber security start-ups develop cutting edge new products and services. I’m pleased to announce the programme is being extended and encourage the nation’s talented entrepreneurs to apply.”