Which singer's 2003 recording helped popularize McDonald's “I'm Lovin' It” campaign?

Justin Timberlake's 2003 recording helped popularize McDonald's “I'm Lovin' It” campaign.

The campaign used a song recorded by Justin Timberlake, with production associated with the Neptunes, while the slogan and musical identity were adapted for McDonald's international advertising. Timberlake's involvement helped connect the campaign with contemporary pop music rather than presenting it as a conventional restaurant jingle.

The most recognizable element of the campaign was the short five-note vocal hook, commonly written as “ba da ba ba ba.” That hook appeared across commercials and became strongly linked with the McDonald's name.

The campaign's music history can be confusing because multiple versions and contributors are discussed in accounts of its development. The answer here identifies the singer associated with the 2003 recording used in the campaign, not the advertising agency or producer involved in creating the broader brand platform.