unnumbered.tex

\documentclass{report}

\usepackage{lipsum}
\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhead[L]{\leftmark}
\fancyhead[R]{\rightmark}
\renewcommand{\sectionmark}[1]{\markright{\thesection.\ #1}}

\usepackage{boxedminipage}

% Redefine the \chapter command:
% \chapter[header]{title}
% \chapter*{title}
% For the \chapter* version, we insert a \markboth command.
% For the non-* version we just pass the arguments to the
% original \chapter command.

\newcommand\originalchapter{}% check that we can define this name
\let\originalchapter\chapter
\RenewDocumentCommand \chapter {som}{%
  \IfBooleanTF{#1}
    {% \chapter*
      \originalchapter*{#3}%
      \markboth{#3}{}%
      % we can also put it in the Table of Contents
      \addcontentsline{toc}{chapter}{#3}
    }%
    {% normal \chapter
      \IfNoValueTF{#2}
        {\originalchapter{#3}}
        {\originalchapter[#2]{#3}}%
    }%
}

\newcommand\originalsection{}% check that we can define this name
\let\originalsection\section
\RenewDocumentCommand \section {som}{%
  \IfBooleanTF{#1}
    {% \section*
      \originalsection*{#3}%
      \markright{#3}%
      % we can also put it in the Table of Contents
      \addcontentsline{toc}{section}{#3}
    }%
    {% normal \section
      \IfNoValueTF{#2}
        {\originalsection{#3}}
        {\originalsection[#2]{#3}}%
    }%
}

\begin{document}
\tableofcontents

\chapter*{Intro}

\noindent
\begin{boxedminipage}{\textwidth}
In this example we show how to get (numbered or unnumbered) chapter titles and unnumbered section titles in the page headers.

We redefine the \verb|\chapter| command. For the \texttt{*} (unnumbered)
version, we add a \verb|\markboth| command and add it to the Table of
Contents. For the non-* (numbered) version we just pass the arguments to
the original \verb|\chapter| command.
%\end{boxedminipage}

%\noindent
%\begin{boxedminipage}{\textwidth}
{\small\begin{verbatim}
\newcommand\originalchapter{}% check that we can define this name
\let\originalchapter\chapter
\RenewDocumentCommand \chapter {som}{%
  \IfBooleanTF{#1}
    {% \chapter*
      \originalchapter*{#3}%
      \markboth{#3}{}%
      % we can also put it in the Table of Contents
      \addcontentsline{toc}{chapter}{#3}
    }%
    {% normal \chapter
      \IfNoValueTF{#2}
        {\originalchapter{#3}}
        {\originalchapter[#2]{#3}}%
    }%
}
\end{verbatim}}
\end{boxedminipage}

\noindent
\begin{boxedminipage}{\textwidth}
{\small\begin{verbatim}
\newcommand\originalsection{}% check that we can define this name
\let\originalsection\section
\RenewDocumentCommand \section {som}{%
  \IfBooleanTF{#1}
    {% \section*
      \originalsection*{#3}%
      \markright{#3}%
      % we can also put it in the Table of Contents
      \addcontentsline{toc}{section}{#3}
    }%
    {% normal \section
      \IfNoValueTF{#2}
        {\originalsection{#3}}
        {\originalsection[#2]{#3}}%
    }%
}
\end{verbatim}}
\end{boxedminipage}

\section*{First (unnumbered) section}

\lipsum

\chapter{Body}

\section{Second (numbered) section}

\lipsum

\end{document}