Cllr Brian Tierney said he withdrew the reference when he became aware of the nature of the charges.
A Derry councillor has apologised for giving a court reference for a soldier who has been jailed for rape.
SDLP councillor Brian Tierney said the reference for Kielan Mooney was a "huge error of judgement".
A serving member of the Irish Army, Mooney (30) of Bloomfield Park in Derry, was jailed for eight-and-a-half years on Monday for raping a female member of the Irish Defence Forces.
Mooney was found guilty at Dublin's Central Criminal Court in December of three counts of rape and one count of sexual assault.
The offences happened in a Dublin hotel in July 2021.
Affidavits which were given as character references for Mooney, with some saying he was a good father to his five children.
During sentencing on Monday, the court was told that two women had supplied statements to dispute the affidavits.
Mr Justice Tony Hunt said Mooney's duties as a father were "grossly overstated" and he would not suspend any portion of his sentence.
Cllr Tierney said he was unaware of the "seriousness" of the case when he wrote the reference.
He said he withdrew the reference when he became aware of the nature of the charges.
The SDLP said Tierney's actions were "entirely wrong" and the party would be issuing guidance to elected representatives "to ensure there is no repeat of this in future".
Cllr Tierney said: "It was a huge error of judgement on my part to issue this personal statement and something I profoundly regret."
The SDLP councillor said he was "not aware of the details of the charges when I wrote it".
"I withdrew the statement when I became aware of the nature of the charges but accept it was a serious failing on my part not to establish the details before writing the statement," he added.
"I offer sincere apologies to the victim in this awful case and anyone who has been affected by my actions.
"I will do everything possible to learn from this experience going forward."
The SDLP said Tierney's actions "were entirely wrong and he has accepted he made a grave error of judgement".
"There is no excuse for giving a character reference for any case involving a crime of this nature," a party spokesperson added.
"The SDLP supports the removal of the use of character references in courts, particularly in cases involving gender-based violence.
"The views of individuals have no place in determining the outcome of a criminal case."
The statement added: "Following this incident, we will be carrying out a review and issuing guidance on representations and references to all elected representatives so that they understand the challenges that victims face in getting justice in cases of gender-based violence and the traumatising impact these references can have.
"We will be making every effort to ensure there is no repeat of this in future."
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