It signals a new era for rugby’s former Celtic League which features the top clubs from Scotland, Ireland, Wales and Italy.
As well as a new title sponsor, the Pro12 has a new TV deal in place with Sky Sports which should raise the league’s profile considerably.
Previously, matches in Scotland were shown on the Gaelic freeview channel BBC Alba.
Guinness has a long association with rugby. It sponsored the English Premiership between 2005 and 2010 and is currently an official partner of Scottish Rugby.
RaboDirect took over from cider maker Magners as sponsor of the Celtic League in 2011, changing the name of the competition to the Pro12. The current champions are Leinster who beat Glasgow Warriors in the final in Dublin in May.
The Pro12’s new TV deal will see Sky Sports broadcast 33 live games per season over the next four years.