Greig was commissioned to write the musical, titled "The Events," for the Actors Touring Company by director Ramin Gray, The Guardian reported Saturday.
Greig said he and Gray traveled to Norway three months after Breivik committed the killings to talk to locals about how the massacre affected them.
"I was most interested in how Norwegian society was feeling," Greig said this weekend. "Oslo is not a huge city and everybody pretty much knows everybody else, so almost everyone we spoke to had been affected. Some people asked us not to write or talk about Breivik. I am not at all certain whether we give him a victory by ignoring him or trying to understand him. That is what I wanted to question."
Because so many people were touched by the killings, Greig said he decided to change the setting of the musical to his native Scotland and not name the killer in the play.
Instead, the musical centers on a woman who, described as being "at the center of the events," who has to decide on her response to the mass murder.
"Breivik's violence was done to an entire society," he added. "I was interested in how people responded. Norway seems to be a poster boy for the liberal West. It represents the Scandinavian social democratic ideal and the attack seemed to be aimed at that."
Breivik, now 34, was sentenced to 22 years in prison, with a possibility of longer incarceration, for killing 77 people in July 2011; eight people were killed in a bombing at a government building on downtown Oslo and another 69 people in a shooting spree on the nearby Utoya island.
"The Events" will premiere at Edinburgh's Traverse Theatre this summer.