For Ulster it will be their first opportunity to compete for the title through a play-off, having last taken the league crown in 2006.
In the three previous play-off finals the top seeds have become champions just once, when Munster defeated Leinster 19-9 at Thomond Park in 2011.
In the other two finals, both held at the RDS, that season's top seeds Leinster were defeated by the second-placed team, the Ospreys. No team that finished lower than second in the table during the regular season has ever lifted the title.
RABODIRECT PRO12 FINAL:
Saturday, May 25 -
ULSTER (1st) v LEINSTER (2nd), the RDS, 4.45pm (live BBC 2 Northern Ireland/TG4/RTÉ Two/BBC ALBA/BBC 2 Wales/SportItalia 2)