The appointment of Hennessy, who will report to Labour's director of comms Bob Roberts, follows the Conservatives hiring Tim Collins for a similar role.
He joins the Labour Party from The Sunday Telegraph after a career that has seen him cover politics for several national newspapers.
In his new role, Hennessy will direct, shape and lead the daily media output of the Labour Party.
The aim is to help sharpen Labour’s attack stories, improve message discipline and ensure the party delivers a 24-hour news cycle.
Ed Miliband, Leader of the Labour Party, said: "I am delighted to welcome Paddy to the Labour Party as our new deputy director of communications.
"His experience working at a range of national newspapers will add significant expertise to the Labour Party’s communications team. I’m looking forward to working with him."
Hennessy added: "I am sad to be leaving The Sunday Telegraph after nine great years but this is an exciting new challenge. After nearly 30 years working in newspapers, it’s a big move but a simple task: to help Labour win the general election. I’m delighted to be joining."