The pair join from Pagan Films, which announced that it is to close earlier this month.
"Rankin & Chris" have worked as a team since 2000. They directed the documentary Rankin's Male Nudes, the comedy-drama Model, Actress, Whatever for Channel 4, and the short film Perfect for FilmFour. In 2003, they began commercials projects, directing campaigns for Dove, through Ogilvy & Mather, Rimmel, through JWT London, and Nintendo, through Leo Burnett. They are currently shooting a campaign for the fashion retailer H&M.
Rankin & Chris recently moved into feature films.
Their film The Lives of the Saints won the Grand Jury Prize at the Salento International Film Festival. It will make its debut in the capital at The Times BFI 50th London Film Festival in October.
As a photographer, Rankin has also shot a number of print campaigns, including the long-running "real faces of beauty" campaign for Dove. His most recent work is a print drive for the Special Olympics, created by JWT London.
Rankin said: "We're delighted to be joining such a strong established name as HSI, with all the support and contacts that it boasts."
Pagan Films was formed by the ex-Godman founder Adam Saward and the director Vaughan Arnell, who was behind ads such as Levi's "creek" and Stella Artois' "the red shoes". Earlier this month, Arnell moved to Blink Productions for commercials representation.
Formerly Exposure Films, HSI London has a roster of directors including Jake & Jim, Matthew Vaughn, Simon Green and Thomas Napper.