The contract, which was split mainly between Maiden and JCDecaux plus several smaller outdoor companies, covers more than 3,100 poster sites in the UK, comprising mostly 48- and 96-sheet sites.
The new contract has been upgraded from seven years to a 10-year deal to avoid expensive pitch processes.
Ron Zeghibe, chief executive of Maiden, said: "This latest £350m contract will complete the concessions that Network Rail has recently put out to tender -- worth in total some £800m in ad revenues over their 10-year duration."
The appointment follows the Network Rail rail-side and platform advertising contracts won by Maiden in July, which were worth a total of £477m in advertising revenue over their 10-year life.
The larger of the two contracts won last year covered more than 2,000 poster sites across 17 mainline stations, including Birmingham New Street, Charing Cross, Euston and Victoria among others, in a deal spanning 10 years.
Maiden has also recently won contracts with National Express Group, South Eastern Trains and First Great Western.
The company also announced it is planning to invest in its Network Rail ad properties over the next 18 months.
"We intend to invest up to £5m in the Network Rail estate over that period to maximise the value of the Network Rail," Zeghibe said.
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