Heart coach John Aloisi confirmed the appointment with Kewell, the man recently voted Australia's greatest ever footballer, to skipper the team in its opening A-League match of the season on Saturday 12 October against his former side, Melbourne Victory.
"It was an easy decision after seeing Harry train here for the past two months," Aloisi said.
Kewell has not been a regular captain of any club previously but did skipper the Socceroos for four games in 2008.
The 34-year-old revealed he would not be the most vocal captain the A-League will ever see but is confident he has much to offer in the role.
"I've never taken (the captain's armband) at club level so for me this is a first-time thing which I'm very very honoured to accept," Kewell said.
"I know it's going to be challenging, I'm looking forward to the challenges ahead.
"I've played under some great captains in my career and learned from them.
"Hopefully I can call upon a few things that they've done when they were captains and I can bring that to Melbourne Heart."
Aloisi believes Kewell's presence alone will lift his team-mates.
"Over the past two months Harry has shown the leadership qualities that we're looking for in a captain," Aloisi said.
"He's been a positive influence on and off the pitch with the players.
"The way he prepares himself as a professional player, he leads by example and on the training pitch he sets high standards and he demands that all the players follow.
"I believe Harry will be a great captain for us this season and I'm looking forward to the season now."
Kewell's appointment comes after Heart shed a number of experienced players, including Kewell's predecessor as captain, Fred, after last season.
Simon Colosimo, Matt Thompson, Richard Garcia and Clint Bolton are others to have departed.
Heart's pres-season campaign continues on Wednesday evening against Oakleigh Cannons at Kingston Heath Soccer Complex, Cheltenham.
Meanwhile, Heart announce that its principal partner, Westpac, had renewed its contract for the next three years.