John McGrogan, 65, from Blackridge, West Lothian, abused the pair over the course of three decades.
A judge heard how the victims finally revealed their ordeals in 2014 after McGrogan was convicted of child porn offences.
He was yesterday returned to the High Court in Glasgow having earlier admitted to raping the girls.
Lord Burns told him that he had “exploited” the duo for his own “gratification”.
He added the victim impact statements given to him had made “harrowing” reading.
McGrogan will also be supervised for a further four years on his release.
The crimes took place between 1981 and 2005 in Edinburgh.
The first girl was aged 11 when she was raped. The other was attacked between the ages of six and 11.
The court heard the “catalyst” for McGrogan finally being snared came in September 2014 after he was convicted of possessing indecent images.
This led to the rape victims coming forward.
Both told how McGrogan would try and spoil them by buying them sweets and computer games.