"Girlfriend" received generally positive reviews from music critics, who complimented its catchiness. The song was a worldwide success, peaking at the top spot of the charts in eight countries, including Canada, the United States, and Australia. It additionally charted in the top ten of most other countries. The song's accompanying music video, directed by The Malloys sees Lavigne portraying three alter-egos, with all of them fighting over the same guy. In June 2007, the song's official remix, featuring American rapper Lil Mama was released. Lavigne performed the song a number of times, including at the 2007 MuchMusic Video Awards, the 2007 Teen Choice Awards, and the 2008 Juno Awards.
The song's success made it a mainstay of pop music in the late 2000s. "Girlfriend" was certified multi-platinum in Australia and the United States. It was the top-selling song of 2007, with over 7.3 million worldwide sales. In 2008, the song became the most viewed video on YouTube, and was the first video on the site to reach 100 million views. Rolling Stone ranked the song number thirty-seven on their list of "Top 100 Songs of 2007" list. Several versions of the song were released with the chorus sung in multiple languages. In 2010, the song was named the ninety-fourth most successful song on the Hot 100 in the 2000s decade.