[6] Its key provisions were 1) a ban on unrestricted ("soft money") donations made directly to political parties (often by corporations, unions, or wealthy individuals) and on the solicitation of those donations by elected officials; 2) limits on the advertising that unions, corporations, and non-profit organizations can engage in up to 60 days prior to an election; and 3) restrictions on political parties' use of their funds for advertising on behalf of candidates (in the form of "issue ads" or "coordinated expenditures").

On December 10, 2003, it issued a complicated decision totaling 272 pages in length, that, with a 5-4 majority, upheld the key provisions of McCain-Feingold including (1) the "electioneering communication" provisions (which required disclosure of and prohibited the use of corporate and union treasury funds to pay for or broadcast cable and satellite ads clearly identifying a federal candidate targeted to the candidate's electorate within 30 days of a primary or 60 days of a general election); and (2) the "soft money" ban (which prohibited federal parties, candidates, and officeholders from raising or spending funds not in compliance with contribution restrictions, and prohibited state parties from using such "soft money" in connection with federal elections).

Justices John Paul Stevens, Sandra Day O'Connor, David Souter, Ruth Bader Ginsburg and Stephen Breyer established the majority for two parts of the Court's opinion: Because the regulations dealt mostly with soft-money contributions that were used to register voters and increase attendance at the polls, not with campaign expenditures (which are more explicitly a statement of political values and therefore deserve more protection), the Court held that the restriction on free speech was minimal.

O'Connor and Stevens wrote that "money, like water, will always find an outlet" and that the government was therefore justified in taking steps to prevent schemes developed to get around the contribution limits.

The Chief Justice's opinion struck down the provision banning political contributions by minors but ruled that the appellants lacked standing with regard to the rest of the challenges to titles III and IV.