Tweed, 53, a father of four, blew kisses and waved to family members as he was led from the dock in disgrace to begin his term behind bars at the high-security Maghaberry Prison in Co Antrim.
There were heated exchanges between Tweed’s supporters and members of his victims’ family during the hearing at Downpatrick Crown Court.
Tweed, who was capped five times for Ireland during the 1990s and played at the World Cup in South Africa, was convicted of 13 counts of abuse, including indecent assault and gross indecency with a child.
The sex abuse spanned an eight-year period from 1988, while he was at the height of his rugby career, and happened when the girls were aged between eight and 11 years old.
Judge Alistair Devlin described the crimes as thoroughly despicable and deeply disturbing. He said they had left a devastating legacy on both women.
Victim impact assessments, some of which were detailed in court, disclosed that one of the girls had attempted suicide, suffered sleep disturbance, and saw her marriage break down.
Judge Devlin said: “The defendant has shown and continues to show no remorse whatsoever in relation to any of these offences.”
Tweed showed no emotion as the sentence was handed down. He stood in the dock flanked by two prison guards with his hands clasped tightly in front of him. At times, when details of the abuse were read out, Tweed, who consistently denied guilt, shook his head.
Tweed, from Clonavon Terrace, Ballymena, Co Antrim, has four children of his own as well as two stepchildren.
Tweed, who also played for Ulster, was first selected to play against France during the 1995 Five Nations and went on to feature in games at the World Cup in South Africa.
However his hardline unionist views made him a divisive character among rugby fans.
Tweed was also a prominent member of the Orange Order and entered politics under Ian Paisley’s Democratic Unionist Party banner after his lodge LOL 496 was prevented from marching through Dunloy during the mid-1990s, close to the village where he grew up. He was a key figure during the bitter sectarian Harryville dispute where loyalists picketed a Catholic church in Ballymena for nine months.
Tweed left the DUP in 2007 over the party’s decision to share power with Sinn Féin and later joined Jim Allister’s Traditional Unionist Voice. He has since been expelled from the TUV.
Last November, the jury of 10 women and two men took two days of deliberation before convicting Tweed with majority verdicts on 13 counts of child sex abuse including indecent assault, gross indecency, and inciting a child to commit an act of gross indecency.
It was not the first time Tweed had stood trial accused of sex abuse. In 2009, he was acquitted of 10 sex abuse charges against two different young girls.