Writing a tutorial on programming, I needed citations within footnotes. Luckily, the biblatex package added support (see first comment on the sourceforge page of biblatex) for citations within footnotes in 2011. Apparently, this is not straightforward, since a low-level citation command has to be used to satisfy LaTeX. Anyway, this is now done automatically by thebiblatex package, so I didn’t have to make any changes.
In my document, I only use the LaTeX command \autocite which behavior I can define in the document preamble. In my preamble I have:
\usepackage[backend=biber,autocite=footnote,style=authortitle-ibid]{biblatex}
\bibliography{bibliography.en.bib}
Now, with the following TeX code…
\chapter{My chapter}
This is a test\footnote{TeX is awesome \autocite[see][p. 120]{Knuth}. I agree.} for
a citation within a footnote. However, this is a citation\autocite[]{Ritchie75} in
normal text.
… you get the following output:
You will notice that footnote 2 is a citation from within the normal text. Since I’ve specified autocite=footnote in the preamble, this is rendered as a footnote. However, the citation from within the footnote 1 is rendered in-line.