Radwanska, 25, has climbed as high as number two in the rankings but a major title has eluded the Pole in her career - her run to the Wimbledon final in 2012 her best effort at a big tournament.
Navratilova will work alongside Radwanska's coach Tomasz Wiktorowski.
Radwanska said Navratilova will be a key asset in her bid to break her grand slam drought.
"I am absolutely delighted that Martina has agreed to help me and my team next season," Radwanska said.
"She is my idol in tennis and I am honoured we will be working together. Her achievements speak for themselves and I hope that I can learn from all her experience.
"My goal is to win a grand slam, so to have someone with Martina's accomplishments in my corner is going to be hugely advantageous and give me a big boost.
"We are originally from a similar part of the world so we share an understanding about tennis and life, which I'm sure will translate into a successful relationship."
Along with her singles major success, Navratilova also won 41 doubles majors - both women's and mixed.
The Czech-born American said she was excited about her move into the coaching ranks.
"I did not sleep very well last night, thinking about getting back into match mode and the competitions," Navratilova said.
"I am really excited about this opportunity to join Agnieszka's team and work with Tomasz and it is going to be a fun challenge. I was delighted when Agnieszka asked me if I would collaborate with Tomasz and I can't wait to get started."
Great Britain's Andy Murray was quick to wish Radwanska and Navratilova well in their partnership, with the two-time major champion a promoter of women coaches having appointed Amelie Mauresmo to his team in 2014.
"Well done to @Martina and @ARadwanska wish them all the best for next year! Hope it goes well for you both," Murray tweeted.
Radwanska is set to launch her 2015 season at the non-tour Hopman Cup in Perth, representing Poland alongside Jerzy Janowicz, starting January 4.
Her first 2015 tour appearance will be at the Apia International in Sydney - a tournament she won in 2013 - in her final tune-up to the Australian Open in Melbourne in January.