The 27-year-old spent last season on loan at Chesterfield, scoring 15 goals in 38 appearances for the Spireites.
Novak has agreed a three-year contract at The Valley and becomes the Addicks' third signing of the summer.
"Lee has shown a consistency at both Championship and League One level and is a proven goalscorer," Charlton boss Russell Slade told the club website.
Novak joined Birmingham from Huddersfield in summer 2013 and scored 12 goals in 69 outings for the Blues.
Meanwhile, Charlton striker Igor Vetokele has joined Belgian Pro League side Zulte-Waregem on a season-long loan deal.
Zulte-Waragem have an option to buy the 24-year-old Angola international as part of the deal.
Vetokele moved to south-east London in the summer of 2014 and scored two goals in 18 appearances in 2015-16.
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Olsson, who played 261 times after joining the Baggies in 2008, would have been out of contract this summer.
But the Premier League club have agreed to cancel his deal early so he can return to his homeland in time for the start of their new top-flight season.
"Albion has, and will always be, a huge part of my life," said Olsson, 34.
"It's all happened so quickly I've not had chance to say a proper farewell to so many people. I will be back at the first chance to do that.
"I'm really grateful to the club for helping me sort out this transfer," said the Swede, who also captained Albion during his near nine years' service to the club.
Meanwhile, teenager Kane Wilson has signed his first professional contract at The Hawthorns, the 17-year-old defender having signed a deal which ties him to Albion until the summer of 2019.
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Dennis Clift, from Chelmsford, Essex, grabbed two-week-old Charlie O'Sullivan from the wreckage of a BMW on the M6 in Warwickshire in 1999.
Ever since he has received a Christmas card from the O'Sullivans and wants to return the gesture.
Searches with local authorities and on social media have come to nothing.
"I've tried everything, Facebook, Devon County Council, but I can't find them," he said.
Mr Clift, who was a breakdown recovery man at the time, was travelling back from Birmingham when he saw Jane O'Sullivan's car in flames on the hard shoulder of the motorway.
"Jane had been in the car with her two children and a baby was still on the back seat," he said.
"I went and rescued him.
"I've received a Christmas card every year since and I'd like to send a card back and they've asked me to come down, but I don't where they live."
Mr Clift parked his truck across the carriageway to stop the traffic until police and fire crews arrived.
Mrs O'Sullivan was treated in hospital for shock and minor burns. Mr Clift, Charlie and Mrs O'Sullivan's 14-week-old daughter Rosie were uninjured.

The John Muir Trust has carried out its latest clean-up of Ben Nevis after the thaw of winter snow.
Last September, trust volunteers found as many as 1,000 banana skins dropped at the summit.
Walkers and climbers were warned that the skins take up to two years to break down and did not biodegrade as quickly as they may think.
Plastic bottle and tissues have also been collected in the latest clean-up.
Sarah Lewis, trust conservation officer, said most walkers and climbers dealt with their litter responsibly.
She added: "But it is clear that some people just don't see the impact that their litter has - 100,000 people climb up Ben Nevis every year, so if even a tiny minority of them leave their litter it can quickly build up."
League One side Charlton Athletic have signed Lee Novak following the striker's departure from Birmingham.
[NEXT_CONCEPT]
West Bromwich Albion's long-serving defender Jonas Olsson has had his contract cancelled to allow him to move back to Sweden to join Djurgarden IF.
[NEXT_CONCEPT]
A truck driver who saved a baby from a motorway fireball is trying to find the boy's Devon family so he can send them a Christmas card.
[NEXT_CONCEPT]
Discarded banana skins are still being found on Britain's highest mountain despite warnings from conservationists.