AUTOSPORT revealed last month that the 2010 Intercontinental Rally Challenge champion was the mystery European driver already working with Hyundai and was in strong contention for a seat in the Korean's firm '14 WRC line-up.
Team boss Michel Nandan underlined that Hanninen was just one of a number of drivers set to work on the Hyundai project this year, and that the 2014 squad would not be revealed for some time yet.
"We're very pleased to welcome Juho on board for our 2013 test programme," he said.
"I'm sure his experience and background will contribute to the project and I'm happy with the job he's done so far.
"We have decided to work with different drivers with unique skills and capabilities this year, which will provide us with valuable feedback for 2014."
Hanninen said his first impressions of the Hyundai i20 were encouraging.
"The first run with the i20 WRC was quite positive for me," he said.
"I'm very impressed with the work the team has done so far in such an incredibly short space of time."
The 31-year-old Finn was a long-time member of the Skoda factory squad, adding the 2011 Super 2000 class WRC crown and the '12 European Rally Championship title to his IRC championship before leaving the Czech marque last winter.
Hanninen then made two WRC starts with M-Sport Ford at the start of this year.