Guardian columnist George Monbiot has agreed to carry out three years of charity work to settle a libel action brought by former Conservative Party chairman Lord McAlpine.
Mr Monbiot was one of a number of Twitter users who falsely linked the peer to claims of child abuse.
The writer, who will do work totalling £25,000, said he was "extremely sorry".
Lord McAlpine's lawyers have already said he will sue Speaker's wife Sally Bercow for libel over a similar tweet.
The peer was falsely accused after a BBC Newsnight investigation into allegations of historical child abuse. He was not named on the programme but was wrongly identified on the internet.
The BBC has already paid £185,000 in libel damages, and ITV £125,000.
'Atmosphere of innuendo'
Mr Monbiot said his settlement with Lord McAlpine was "eminently decent".
In a statement on his website, he said: "I accepted the suggestion immediately and without reservation. I feel the proposed settlement reflects very well on Lord McAlpine, who is seeking nothing for himself, but wants to see work done which could be of great benefit to others."
Mr Monbiot, who had 55,000 followers at the time he posted the tweets, said he had done a "stupid and thoughtless thing".
"In doing so, I helped to stoke an atmosphere of innuendo around an innocent man," he added.
The money will go to three charities of Mr Monbiot's choice. He said he was keen to work with children's and environmental charities.
Lord McAlpine announced last month that he was dropping his defamation claims against Twitter users with fewer than 500 followers and would instead ask for a charitable donation.
A spokesman for the peer said he was pleased to have reached a settlement with Mr Monbiot.