The SRU website reports that Grainger, who is currently the Tournament Director of both the Celtic League and the Celtic Cup, succeeds Phil Anderton who was promoted to Chief Executive of Scottish Rugby in February.
Phil Anderton said: "We advertised two posts - Commercial and Marketing Director and Director of Professional Rugby - but in the light of Keith's considerable experience in professional rugby and the outstanding commercial growth which he has overseen at four of the UK's top professional clubs, he will be able to fulfil both remits.
"In Keith we have been very fortunate to have found an outstanding candidate who has the required experience. He will be responsible for driving up Scottish Rugby's commercial revenues and also heightening interest and participation in our sport in Scotland at all levels.
"In addition, Keith will have the responsibility for all off-the-field operations of Scottish Rugby's three professional teams and for the development of plans for the growth of the professional game in Scotland. On the field matters at our three professional teams will be overseen by our Director of Rugby, Ian McGeechan, with whom Keith worked at Northampton."
The new structure therefore makes a clear distinction between on the field activity and commercial performance.
Grainger who was formerly the Chief Executive of both Newport RFC and Northampton Saints had previously been the commercial driving force at Leicester Tigers and Newcastle Falcons. At Newcastle he attracted two sell-out crowds for their Tetley Bitter Cup games against West Hartlepool and Leicester Tigers despite the Falcons’ second division status. At Leicester Tigers he delivered an increase in turnover of 50% in his first year, at Northampton in 1999 he pioneered the club's first ticket and membership office and increased both crowds and gate receipts significantly.
Grainger has brought a buzz to every club with which he has been connected; most notably during his tenure at Newport where he introduced the tented Family Village and the much admired Gateway community programmes, trebling revenues in just two seasons and overseeing increases in crowd attendance from just around 1,000 spectators to an average in excess of 8,500 per game.
Since May 2003 he has been the Tournament Director of the Celtic League - the flagship professional tournament of the three Celtic unions - and Celtic Cup, where he has overseen a growth in commercial income and an increase in supporters through the turnstiles.
Grainger, who is no stranger to Scotland having been based at Penicuik, Stirling and Edinburgh during his eight year career with Procter and Gamble, said: "I am hugely excited by the challenges offered by my new role. Scottish Rugby has ambitious plans for the growth of the sport in Scotland and I am looking forward to playing my part in delivering that dynamic future."
John Hussey, Chairman of the Celtic League Association, said: "I would like to record my thanks to Keith for his contribution to the ongoing development of the Celtic League and Celtic Cup over the last 17 months. The tournaments are widely regarded as being competitive, credible and professionally run and I am delighted that Keith will be continuing his association with the Celtic League."
The Celtic League Association has identified a number of exceptional candidates for Keith's replacement and an announcement will be made in due course.
As the post of chief executive at the three professional teams is redundant, Scottish Rugby will be offering appropriate support and assistance to the three individuals who held that position.