The 151-year-old Royal Albert bridge which links Devon and Cornwall will be refurbished following building consent.
Plymouth City Council and Cornwall Council (CC) approved plans to strengthen and refurbish the bridge designed by Isambard Kingdom Brunel.
Network Rail will carry out the work over three years when trains are not running, to minimise disruption.
Graeme Hicks from CC said: "It's only fitting that such a legendary piece of engineering should be preserved."
Repairs will be made to corroded parts of the grade 1 listed structure and efforts will be made to replicate the original design, by using special bolts similar to Victorian rivets.
The bridge will also be re-painted goose grey, the same colour it has been since 1911.
Mr Hicks said: "This is an historic structure that provides the gateway into Cornwall for millions of people every year, and I'm delighted to see this work taking place."
It is estimated that the cost of the refurbishment will be about £10m.