"I am sorry. Without reservation or qualification. I apologize to the Romney family," she wrote on Twitter, using the hashtag "#MHPapology."
"I work by guiding principle that those who offend do not have the right to tell those they hurt that they r wrong for hurting," she continued. "Therefore, while I meant no offense, I want to immediately apologize to the Romney family for hurting them."
In the Sunday segment, Harris-Perry had panelists caption the photo. She joked that Kieran Romney would marry Kanye West's daughter, North West.
"Could you imagine Mitt Romney and Kanye West as in-laws?" she asked.
On Tuesday, the MSNBC host explained she came from a similar background and that she meant no offense.
"As black child born into large white Mormon family I feel familiarity w/ Romney family pic & never meant to suggest otherwise," she said, again adding the hashtag "#MHPapology." "I apologize to all families built on loving transracial adoptions who feel I degraded their lives or choices."
The segment drew strong criticism from many on the right, including former Sen. Scott Brown (R-MA), a Romney family friend, Republican National Committee Chairman Reince Priebus, and former Alaska Gov. Sarah Palin (R), who was the subject of another controversial MSNBC segment that led to the resignation of host Martin Bashir.