Peter Collins abused young girls for two decades until one of his victims found the courage to speak out.
The “predatory” 58-year-old, of Talfourd Street, Bordesley Green, denied the claims against him and said he had a condition which caused him to fall asleep and not know what he was doing.
But his cover story was dismissed by jurors who convicted him of 12 charges after a three-week trial at Birmingham Crown Court.
He was jailed for 19 years and ordered to register as a sex offender for life on Monday.
Collins began his abuse in 1995 on a girl who was aged 11 at the time, West Midlands Police said.
He then sexually assaulted two other girls, with his last recorded assault being on a 12-year-old girl, which was reported in 2016.
One of the victims speak out about her ordeal the same year, and the police began an investigation.
Collins was convicted of three counts of indecent assault, one of indecency with a child, two of sexual assault with a child under 13 by penetration, two of assault by penetration, two of sexual assault and two of causing or inciting a child to engage in sexual activity.
Investigating officer, Det Con Katrina Sands, from West Midlands Police’s Public Protection Unit, said: “Collins abused vulnerable young girls and continued his predatory behaviour for over several decades.
All victims gave evidence in court and I commend their bravery in re-living what are surely very painful memories.
“When confronted, Collins denied the allegations and claimed in his defence that he had a condition which led to him fall asleep unexpectedly in a number of places and being unaware of what he was doing.
“Expert witnesses gave evidence which didn’t support this claim.
“We are delighted the jury saw through Collins’ denial the offences had happened and this now means he will be a registered sex offender for the rest of his life.
“We hope that anyone else who may have been abused by him now has the courage to come forward.”