The 25-year-old Malik, who has played 18 Tests and 137 one-day internationals, was unveiled at a press conference here as captain of the Test and one-day squads until the end of 2007.
"He is the future of cricket. He has intelligence and he has a good cricketing mind," Pakistan Cricket Board (PCB) chairman Nasim Ashraf told reporters.
"Malik is the personality to get the best from players both senior and junior," Ashraf added. "He is a unanimous choice. He is the best man to lead the team."
Malik's first challenge is due to be a three-match one-day international series against Sri Lanka next month.
"I am very motivated. I will give 110 per cent," Malik told the press conference. He added that the team was 'very good' but needed a stable opening pair and to improve its fielding.
Talat Ali was meanwhile appointed manager of the Pakistan cricket team for two years, Ashraf said. No decision has been made on a vice-captain.
The appointment of the relatively inexperienced Malik came after senior batsman and former vice-captain Younis Khan refused to assume the leadership role for personal reasons.
PCB sources said they opted for the right-handed batsman and useful off-spinner over more established names like master batsman Mohammad Yousuf because they wanted a fresh start.
Malik is likely to face pressure to deliver and command a team which has several captaincy hopefuls including Yousuf, flamboyant pacer Shoaib Akhtar and mercurial all-rounder Shahid Afridi.
Pakistan, the World Cup winners in 1992, were knocked out of the current edition in the Caribbean after losing to minnows Ireland on March 17 in one of the biggest upsets in the tournament's history.
The following day coach Bob Woolmer was found murdered in his Jamaica hotel room. An overwhelmed Inzamam announced his retirement from one-day cricket and relinquished the captaincy soon afterwards.
Malik, from the industrial town of Sialkot near the Indian border, has a batting average of 37.64. He made his debut against Bangladesh in 2001.
His bowling action has been reported twice, once in 2005 and then again in 2006, forcing him to undergo elbow surgery.
The only other blight on his career so far was when Pakistan cricket chiefs banned him for one Test in 2005 for throwing a domestic game in protest after his team was penalised for a slow over rate in another match.
He later apologised and told Thursday's press conference: "I have explained that at various times and this is not the time to dig up the past, but to look ahead for the future."
Immediate reaction to his appointment was mixed.
Former Pakistan paceman Sarfraz Nawaz said the "decision is disappointing," adding: "Nasim Ashraf has been taking one decision after another towards the destruction of cricket in Pakistan."
However former PCB chief Tauqir Zia played down Malik's inexperience. "It appears to be a good choice. He is not very new, he has been playing for quite some time," he told a private television channel.
Former captains Imran Khan and Intikhab Alam on Wednesday said that choosing Malik would be a risk because of his age.
The announcement of Malik as captain comes a day after new chief selector and former Test off-spinner Salahuddin Ahmad warned all-rounders that his priority would be pick specialists to improve the team's performances.