Wearing a navy suit, maroon tie and his wedding band, a tearful Weiner, 52, described his conduct before U.S. District Judge Loretta Preska in New York City.
"I have a sickness, but I do not have an excuse," Weiner said, apologizing to the 15-year-old girl to whom he sent sexually explicit images and messages last year.
The charge of transferring obscene material to a minor carries a maximum sentence of 10 years in prison, but Weiner is likely to get less. As part of his plea agreement, federal prosecutors said they would consider a term between 21 months and 27 months "fair and appropriate."
Weiner will be sentenced on Sept. 8.
The former Democratic congressman's political career imploded after a series of scandals involving inappropriate sexual exchanges with women online.
The probe into his exchanges with the teenage girl, however, also helped upend the final days of the 2016 U.S. presidential campaign.
Federal agents who had seized Weiner's laptop discovered a batch of emails from Huma Abedin, a senior aide to Hillary Clinton, the Democratic nominee for president in 2016.Read more at Reuters