The 29-year-old led Sarries to the Premiership and European Champions Cup titles last season while Hargreaves was sidelined through injury.
Barritt has made 171 appearances since joining Saracens in 2008 and has won 26 international caps for England.
Director of rugby Mark McCall said Barritt had shown "exceptional leadership qualities".
The Ulsterman continued: "He is ideally qualified to be our captain.
"Brad is someone who leads through example - through his actions, attitude and application. He is one of the most competitive players I have ever come across.
"He stepped in to the captaincy role last season in Alistair's absence with real aplomb."
Saracens begin their defence of the Premiership title against Worcester on Saturday, 3 September while the north London side have been drawn to face Toulon, Sale and Scarlets in the pool stage of the Champions Cup.
Double winners Saracens have appointed centre Brad Barritt as captain, replacing Alistair Hargreaves.