Jamie Rudling, 28, from Dunoon, repeatedly raped one victim, between 2003 and 2011, at an address in Argyll.
He also raped a 22-year-old woman while she was asleep, in Argyll in 2014.
At the High Court in Glasgow, Rudling was jailed for a minimum of three years and six months and told he may never be judged safe enough to be released.
Passing sentence, judge Judge Lady Carmichael told Rudling: "You present a high risk to the public at large if you are at liberty.
"You were sexually offending while on an extended sentence which was intended to protect the public."
Lady Carmichael told Rudling that he showed a pattern of sexual offending from his teenage years and added: "It is significant that your pattern of serious sexual offending became as excessive as it did over a significant period."
She added: "I am imposing a life-long restriction order. It is possible you many never be released. It will be up to the parole board to decide if he is ever released."
Rudling was given three years probation in March 2010 after being convicted of attempting to rape a sleeping woman.
He was also jailed for 28 months at Ayr Sheriff Court in November 2011 and placed under supervision for two years after he persuaded two teenage girls to expose themselves on a webcam.
He also arranged to meet one for sex at Braehead Shopping Centre in Renfrewshire.
Following his conviction, Rudling's counsel unsuccessfully argued for him to be given an extended sentence rather that a life-long restriction order.
Lady Carmichael dismissed imposing an extended sentence saying: "That has been tried already and there was re-offending."

The 58-year-old school principal from Dublin won 144 out of a possible 278 votes and was 98 ahead of his nearest rivals Sean Walsh and Frank Burke.
Horan will take over from current president Aogan O Fearghail in 2018.
"Aogan is the president for the next 12 months so I'll support him and learn from him as best I can," said Horan at Croke Park.
The other candidates for the post were Martin Skelly with 22 votes while 20 went to Robert Frost.
This weekend's annual congress will be dominated by new championship proposals in football and hurling.
The plans put forward by GAA director general Paraic Duffy include completing the All-Ireland Senior Championships by the end of August.
Also included is a new round-robin format for the All-Ireland SFC quarter-finals, which would mean more games.
This proposal has proved particularly controversial in recent weeks.
Both the Gaelic Players' Association and recently formed Club Players' Association have come out against Duffy's plans, although not necessarily for the same reasons.
Ostensibly, the main reason for these mooted changes is to try and ensure more regular games for club players but there is a certain  amount of bafflement as to how this can be squared with the motion to have a round-robin stage in the All-Ireland Football quarter-finals.
The new club players' body has been angered after the GAA's top brass refused to grant it a speaking platform at the Croke Park gathering.
However, that may change at further annual gatherings of GAA delegates if a motion for the club players' body to be officially recognised is passed in Dublin.
All the indications are that the votes on both the so-called new 'Super Eight football round' and the proposal to bring forward the All-Ireland finals will be exceptionally close, with a two-thirds' majority required for the format changes to be tried for a three-year period.
To make matters even complicated, congress will also hear a number of motions calls from the two-thirds majority to be scrapped, with one call suggestion a simple majority and another calling for the figure to be lowered to 60%.
Inevitably, those motions will require a two-thirds majority to be passed.
Going into the weekend, Croke Park's desire for replays to be scrapped - in favour of extra-time - in all championship games bar provincial and All-Ireland finals looks likely to be comfortably passed.
At last year's congress, motions to move All-Ireland Finals to earlier in the year and scrap replays were both defeated, although the finals proposal fell narrowly short after getting support from 60.8% of delegates.
A man who raped two women - one of them while he was on probation for grooming two teenage girls - has been handed a lifelong restriction order.
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John Horan easily won the vote at Congress on Friday night to become the GAA president-elect.