The song appears as the tenth track on the North American edition of the album and lasts for one second less at . It was composed in the key of E Major using common time at 60 beats per minute. Instrumentation consists of a piano, guitar, strings, and "subtle" percussion. The style in which "Don't Let Me Down" was produced received comparisons to song recorded by Timberlake, including "Cry Me a River" and "What Goes Around... Comes Around". According to Michael Cragg of musicOMH, Lewis is singing about "making tough decisions and trying to take back control". Cragg wrote that "Don't Let Me Down" and another "Echo" track "I Got You" are "equally infectious"; he also praised Lewis' vocal performance and described it as "genuinely stirring". Nick Levine for Digital Spy was brief in his description of the song, simply calling it "lovely". BBC Music's Mike Diver wrote that although the track resembles Timberlake's songs "Cry Me a River" and "What Goes Around... Comes Around", Lewis fails to deliver "Don't Let Me Down" with "any comparable soulfulness." As part of his review of "Echo", Matthew Cole for "Slant Magazine" wrote that too much of the album is dominated by "thoughtless" ballads like "Stop Crying Your Heart Out" and "Don't Let Me Down". While he noted that Lewis gives a "technically unimpeachable" vocal performance, he wrote that it does not compensate for the "dull arrangement" and lack of emotion in her delivery. Lewis performed "Don't Let Me Down" at the Rock in Rio festival held in Lisbon on 22 May 2010. The song was included as the second song on the set list of her debut concert tour, called The Labyrinth (2010). It was later included on the DVD release of the tour, "". Lewis performed the song in the first section of the set list, along with "Brave" as the opener, "Better in Time", "Whatever It Takes" and "Take a Bow". Jade Wright for the "Liverpool Echo" wrote that the singer belted out the track. The set was decorated in the style of a castle; acrobats performed as they were hanging from the ceiling on large pieces of fabric while Lewis wore a gold sequined dress and thigh high boots. Credits adapted from the liner notes of "Echo".