Combining this answer of lockstep and this answer of mine, you can add the following lines to change and to & globally
\renewcommand*{\finalnamedelim}{%
\ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
\addspace\&\space}
and the following lines to change and to , in the bibliography
\AtBeginBibliography{%
\renewcommand*{\finalnamedelim}{%
\ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
\addspace\addcomma\space}%
}
MWE:
\documentclass{article}
\begin{filecontents}{\jobname.bib}
@misc{A01,
author = {Sutherland and Varnam},
year = {2001},
title = {Title},
}
\end{filecontents}
\usepackage[style=authoryear,backend=biber]{biblatex}
\renewcommand*{\finalnamedelim}{%
\ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
\addspace\&\space}
\AtBeginBibliography{%
\renewcommand*{\finalnamedelim}{%
\ifnumgreater{\value{liststop}}{2}{\finalandcomma}{}%
\addspace\addcomma\space}%
}
\addbibresource{\jobname.bib}
\begin{document}
Here we cite \cite{A01}.
\printbibliography
\end{document}
Output:
