In May 1993, she was first elected to Craigavon Borough Council for the Loughside District. She sat on all committees and was chair of Technical Services and Environmental Services. In 1996, she was an unsuccessful candidate in the Northern Ireland Forum election in Upper Bann.[3]
In May 1997, she was re-elected to Craigavon Borough. She was elected deputy mayor in 1998 and, from 1999 to 2000, was the first SDLP mayor of Craigavon.[4] Kelly was also deputy leader of the SDLP from 2011 to 2015.[5]
In 2004, Kelly was the target of death threats from dissident Republicans and her home was attacked.[6] In 2009, Kelly was threatened by a masked gunman while canvassing in the Kilwilkie estate in Lurgan.[2]
In 2003, Kelly was elected to Northern Ireland Assembly for Upper Bann. She was a member of the Northern Ireland Policing Board.[7] She lost her seat in the 2016 Assembly election[8] but regained it and rejoined the Policing Board in 2017, at the expense of Sinn Féin.