Chavan, a loyalist Congressman will head the government in Maharashtra while Nationalist Congress Party's Chagan Bhujbal will be the deputy chief minister.
The announcement by senior Congress leader Pranab Mukherjee came after revenue minister Narayan Rane lashed out at the Congress for the delay in naming a man for the top job.
Accepting Congress president Sonia Gandhi's decision to make him the new chief minister, Chavan said "we will ensure that steps will be taken to make people feel safe."
"This is a challenge. This is a great responsibility. Maharashtra needs a tough administration so these things do not happen again," he said.
He also refused to join issue with Narayan Rane, one of the contenders for the chief minister's post.
"I don't want to comment on what Rane has said because people of Maharashtra are not interested in who becomes the CM. Right now, the priorities are different. We have to give the people of Maharashtra confidence so that they feel safe and secure. We have to understand the seriousness of what has happened," he said.
Rane had earlier hit out for the way in which the whole process of selection was done. He also alleged a conspiracy within the Congress against him.
"What is the qualification of Ashok Chavan except that he is the son of a former CM?" Rane asked.
Ashok Chavan, 55, is the son of veteran Congress leader S B Chavan and it is the first time in the state's history that a son and father will have sat on the chief minister's chair.