In my Bibliography, I need two categories: Primary Sources and Secondary Sources. The first needs to be subdivided into Manuscripts and Published Works.

So, I thought I could use the following code:

\printbibheading


This, however, gives me three categories, but I would like to have only two with the first being subdivided. In other words I need something like this:

\printbibliography[keyword={Manuscripts},
title={Primary Sources},
subtitle={Manuscripts}]  %% subtitle={...}


Well, you could do the following to put both sectioning commands in one \defbibheading:

\documentclass[12pt]{article}
\usepackage{biblatex}
\section*{Primary Sources}
\subsection*{Manuscripts}}

\begin{document}
\nocite{knuth:ct}
\end{document}


A fuller example would be:

\documentclass[12pt]{article}

\usepackage[backend=biber,style=authortitle]{biblatex}
\section*{Primary Sources}
\subsection*{Manuscripts}}

\subsection*{Published Works}}

\section*{Secondary Sources}}

\DeclareBibliographyCategory{mss}
\DeclareBibliographyCategory{pri}
\DeclareBibliographyCategory{sec}

\begin{document}

\nocite{knuth:ct,knuth:ct:a,knuth:ct:b}

\end{document}


But for some reason it does not work correctly if you use three bibliography categories, though it will work if you use notcategory.... However, it does work fine with three different keywords (e.g., keyword={mss}, keyword={pri}, keyword={sec}) as long as your .bib file entries have the appropriate keywords field. (Unfortunately, the biblatex-examples.bib that ships with biblatex only has two categories of keywords: primary and secondary.)

Necro'ing after four years because I had a similar problem and found a better solution. Biblatex 3.5 allows to improve the solution a tad. From the manual:

OK, that is not very clear, but what it means is that you can write a macro to produce the bibliographic heading. In the above case, one could do something like:

\defbibheading{firstlevel}[]{%
\section*{#1}

\subsection*{#1}
(...)
\section*{Primary Sources}

\printbibliography[keyword=secondary, heading=firstlevel, title = {Secondary Sources}]


You still need an explicit call to create the second section; maybe a LateX-guru could refine the code definitions to avoid this. But I would argue this solution is cleaner.

I know, I could use something like this:

\printbibheading
\section*{Primary Sources}
\subsection*{Manuscripts}