Owner GWR has ploughed the money into the national station following last week's Rajar report, which revealed that Classic has boosted its audience by 300,000 listeners to report a total of 6.54 million.
The campaign will target 10 million people through TV, print and radio activity as well as direct marketing and is the station's first push of this kind.
It will also involve its branded magazine and TV channel, as well as its books and CDs.
It is hoped to coax listeners from easy listening and speech stations as well as BBC Radio 3, which has branched into more jazz and world music.
The station itself will be bolstered in the coming months with new features including Composers' Notes with John Suchet, The Classic FM Guide to the Orchestra , hosted by violinist Nicole Wilson, and Backstage UK , which will consider British arts organisations.
A series of initiatives "to engage new audiences with the live classical music experience" will also be launched with a number of orchestras from around the UK.
Roger Lewis, managing director and programme controller at Classic FM, said: "We believe in classical music. We have shown that it can be part of everyone's lives. It's time to shout about it."