For most of the 20th century, Franklin County was a Republican bastion, as has long been the case with most of central Ohio. From 1896 to 1992, it went Republican all but five times. However, it has gone Democratic in every election since 1996, reflecting the Democratic trend in most other urban counties nationwide. Columbus and most of its northern and western suburbs lean Democratic, while the more blue-collar southern section of the county leans Republican. From 1996 to 2004, Democratic nominees carried the county by single digit margins, but it swung significantly in favor of Barack Obama in 2008. The county has swung towards Democrats in every subsequent Presidential election, with each candidate breaking the previous county record for both largest Democratic vote share and largest Democratic margin of victory in county history. Most recently, Democratic nominee Joe Biden won the county with 64.7 percent of the vote and a 31.4 percent margin of victory.

In Congress, it is split between three districts. Most of Columbus itself is in the 3rd district, represented by Democrat Joyce Beatty. Most of the northern and eastern portions of the county are in the 12th district, represented by Republican Troy Balderson. The southern portion is in the 15th district, represented by Republican Mike Carey.