The opportunity arose after Cram's regular driver Eric Salignon had been given a 10-place grid penalty for this weekend's first race after stewards decided the Frenchman had caused an avoidable collision at the start of the second race at Donington Park.
Hanley has been competing with Cram in Italian Formula Renault, securing five victories, while still continuing his successful karting career. He has also made selected appearances in the Formula Renault UK and Eurocup series but has only started 19 single-seater races.
The Briton is not daunted by moving up from 200bhp Formula Renaults to the 425bhp World Series machines.
He told Autosport-Atlas: "It is a big jump but it is too good an opportunity to turn down. This weekend will be about gaining useful experience in the World Series and more powerful cars.
"I haven't had any testing but there will be free practice on Thursday. Kimi Raikkonen stepped out of Formula Renault into Formula with only a few car races too. We'll take it as it comes."
The World Series by Renault grid will have 30 cars for the first time this weekend, with Frenchman Patrick Pilet taking the vacant seat at GD Racing. Pillet drove the first half of the season with Jenzer Motorsport.
The 2015 Formula Renault 3.5 season will be notable for being the last with the French company's backing but also produced a worthy champion in Oliver Rowland. PETER MILLS evaluates this year's crop of drivers
Last year's field was extraordinary and hard to match, but the Formula Renault 3.5 grid will still have plenty of talent this season. Glenn Freeman runs through the field ahead of this weekend's season opener
Landing the Fortec seat that took rising star Robin Frijns to the 2012 FR3.5 title was already a good sign for Stoffel Vandoorne. Then McLaren took him under its wing. Peter Mills tells Vandoorne's story so far