"Mercy" garnered overwhelming acclaim from critics, often being praised for its catchy bass line and "summery", jazzy themes.
Digital Spy gave the single a positive review, noting that the single was "a catchy, danceable Northern soul pastiche" and that the "baseline practically reeks of sweat and stale cigarette smoke".
The Times in a review for
Rockferry said that "Mercy" is "a slight but darned catchy number" and "a classic radio hit". The reviewer also drew comparisons between "Mercy" and
Amy Winehouse's critically acclaimed single "
Rehab".
PopMatters said that the song was "still grounded in a bouncing Motown rhythm but [with] the added colour of jaunty keyboards", whilst again comparing the song to "Rehab".
The Observer, in an extremely positive review for
Rockferry, said that "Mercy" "is a big, booming, finger-wagging sashay worthy of the
Supremes". In a positive review for
Rockferry, American music magazine
Billboard said that "Mercy" "is about as summery as summery gets".
NME, giving
Rockferry a negative review, had a mixed attitude towards "Mercy", comparing the song's "Austin Powers organ" to work by
Aretha Franklin.
Slant said that the song has a "bass-heavy syncopated beat, "Yeah, yeah, yeah" refrain [and an] obvious '60s-pop frame of reference". However, the song was given negative comparisons to
Amy Winehouse. "Mercy" also appeared on various critics' "Top" lists. Bill Lamb of
About.com placed "Mercy" at number 29 in a list of his favourite 100 songs of 2008. Fred Bronson of
Billboard placed "Mercy" at number two, whilst the magazine's Keith Caulfield placed "Mercy" in an alphabetical list of his favourite songs of 2008.
Awards and other recognition "Mercy" won the
2008 MOJO Award for Song of the Year. The single was nominated for a
BRIT Award in 2009, for
Best British Single. Duffy's performance of "
Warwick Avenue" at the ceremony helped to increase sales of "Mercy" by double the market average before the broadcast. The song was also nominated for a
Grammy Award in the category "
Best Female Pop Vocal Performance".
Q Awards (Best Track) and the 2009 Music Producers Guild Awards (UK Single of the Year). "Mercy" was also nominated for PRS for Most Performed Work and Best-selling British Song at the 2008
Ivor Novello Awards, winning in the former category. The song was the fourth most played anywhere in the United Kingdom in 2009, revealed in a list compiled by music body PRS. ==Chart performance==