It's recent-ish. I don't remember hearing it much before fifteen years ago or so. But it's definitely an American term, not a British one.

It's come more into vogue because there used to be a much less clear definition of what a showrunner was and their responsibilities. Gene Roddeberry was the creator and executive producer of STAR TREK, for example, but the day-to-day running of the show was handled by different people. However, since the early-to-mid 1990s it's become much more common for one or two people to be identified as being 'in charge' of a show.