Alan Morrison, 47, was told he must serve a minimum of nine years before being eligible for parole.
He is already serving an 18-year jail sentence for the attempted murder of Frederick Paul Stephens beneath the railway arches at Bridge End, Brighouse, in March 2006.
Mr Stephens was shot three times in the stomach and leg because of an allegation of sexual abuse made against him.
Jailing Morrison for the gang rape along with his co-accused, Kevin Wright, 38, who was sentenced to 18 years and David Potts, 60, who got 12 years, Judge Scott Wolsten-holme at Leeds Crown Court said: "These were dreadful offences over a prolonged period in which two very vulnerable children were subjected to sexual abuse in circumstances of a gross breach of trust."
Following a trial at Bradford Crown Court last month, Morrison was found guilty of raping the girl on two occasions between July 2003 and March 2004 and two charges of gross indecency by making an older girl watch them.
Caroline Wigin, prosecuting, said Morrison, who refused to attend his trial or sentencing hearing, has previous convictions for sexual offences dating from 1977 and 1988.
In 1977 he was convicted in Scotland of sodomy and lewd behaviour on a 13-year-old boy and in 1988 he was jailed for 18 months after being convicted of the indecent assault of a 13-year-old girl.
Judge Wolstenholme said: "He poses a very serious risk to the public."
He added: "I hope the public won't be misled in thinking he will be released after nine years – he won't be released until he is no longer a danger to the public."
Wright, of Portwood Street, Heaton, Bradford was convicted of the same offences and Potts, of Driffield, East Yorkshire, was found guilty of two rapes.
A fourth man, Graham Blowers, now dead, was also involved in the abuse.
The older girl told police that the men took it in turns to rape the girl while the other two held her down.
Julie Ogg, of Bradford, another co-defendant was jailed for 18 months for two offences of child cruelty.