Rendell joined members of the group CeasefirePA outside of the Center City offices of Lehigh Valley Republican senator Pat Toomey.
The group is calling on Toomey to support expanded background checks for prospective gun buyers.
A spokesperson for the senator released the following statement Tuesday morning:
"Senator Toomey appreciates hearing from Pennsylvanians on public safety and firearm policy.
"He is talking to many people in the commonwealth and his colleagues in the Senate in hopes that we can improve our background check system while also protecting second amendment rights."
In Washington, Democrats were holding a lunchtime meeting Tuesday to assess whether Sen. Joe Manchin, D-W.Va., had reached an acceptable compromise on gun control legislation, or had a realistic chance of getting one, with Toomey.
Party leaders were giving Manchin until later Tuesday to complete the talks, and a decision by Democrats seemed likely in the next couple of days.
An agreement between the two senators, both among the more conservative members of their parties, would boost efforts to expand background checks because it could attract bipartisan support.
Abandoning those negotiations would put Democrats in a difficult position, making it hard for them to push a measure through the Senate and severely damaging Obama's gun control drive.
The Associated Press contributed to this report.