Songfacts®:

• This song was largely written by guitarist Mick Jones, and appears to be autobiographical for the most part. Around the time it was written, Jones was having a tough time in life - just before Christmas 1978 his flat was broken into and a lot of his possessions stolen. Soon after, his relationship with Slits guitarist Viv Albertine finally ended, leading to a brief period of depression in early 1979.
• The lyrics are sad and depressing, but heavily defiant. They describe a narrator who has taken a rough deal in life but is putting on a brave face and facing life head on ("I've been beat up, I've been thrown out, but I'm not down, I'm not down").
  
  There is a specific section where Mick Jones refers to an incident in 1978 where he was attacked by a gang of rockers in the street:
  "On my own I faced a gang of jeering in strange streets
  When my nerves were pumping and I Fought my fear in
  I did not run, I was not done"
• The song was introduced live in July 1979 in the London shows, although it only lasted in the set for three months - possibly because Mick Jones was on the road to recovery in life, although this is contradicted by the fact that he wound up writing the equally sad "Train in Vain (Stand By Me)" not long after "I'm Not Down."
  
  Before its live debut at the Notre Dame Hall in July 1979, singer Joe Strummer jokingly asked the audience if anyone was contemplating suicide.