The song received positive reviews, praising the song for its lyrics and its catchiness. Nick Levine of Digital Spy gave the song a positive review stating: "Quirky? You betcha, but the result is also a lovely summery pop song - just one of many lovely summery pop songs on Doolittle's upcoming album."
The music video was shot in Jamaica. It shows Doolittle travelling to different places within a Jamaican town by bus and motorbike. The video ends with her sitting in a dinghy after throwing a suitcase into the sea (an interpretation of the lyric "pack up your troubles in your old kit bag and bury them beneath the sea").
"Pack Up" debuted on the Irish Singles Chart at number 15 on 9 July 2010, marking Doolittle's first top 40 hit in that country. The following week the single rose a single place to number 14 and later peaked at number 6.
The single also debuted on the UK Singles Chart on 11 July 2010 at number 12, beating previous single's "Skinny Genes" peak of number 22, the next week it climbed to number 8 making it her first top 10 hit. On the third week in the UK Singles Chart, the single rose to number 5.
In early 2011, the song has featured on British television in the advertisement for Kinder Surprise. The song is also used in a Brazilian soap opera called Insensato Coração and it is included on the soap opera's soundtrack. It was featured on the season 2 premiere of "Mob Wives". It was also played in the background of Cher Lloyd's audition on The X Factor UK in 2010. It was also used in the closing credits to the last live edition of ITV's coverage of the 2010 Tour De France.