Ahir and his wife Sangeeta were accorded a warm welcome to the Sena fold by President Uddhav Thackeray, Yuva Sena chief Aditya Thackeray and other senior leaders at a function in the Thackeray residence 'Matoshree' in Bandra.
The Thackerays tied a symbolic 'Shiv Bandhan' on Ahir's wrist, presented a bouquet and handed over a party flag amidst loud claps and cheers by the gathering.
The Sena chief said that it was not the Sena's policy to "break other parties", but those who willingly came forward to join the party were always welcome.
"With entry of Sachin bhau, the strength of the Sena will increase. He will not regret his decision to join our party," he said.
On his part, Ahir, 47, said he was highly impressed with the work of Thackeray for the 'Marathi manus', for developmental issues concerning the common masses which prompted him to take the decision to join the Sena.
"Thousands of Shiv Sainiks were calling me to join the Sena. I shall take up any responsibility given by the party and contribute to its growth and expansion," Ahir said, adding that "NCP President Sharad Pawar will always remain in my heart".
Criticising the move, NCP national spokesperson Nawab Malik said those who have no strength to fight, jump into the flow. He said the Congress-NCP will perform better than the ruling Bharatiya Janata Party-Sena in the next elections.
Earlier in the day, former minister Ahir told the media that "in politics, tough decisions have to be taken and he was pained over his decision", which comes barely two months ahead of the state assembly elections.
However, the legislator from Worli said he was happy to get an opportunity to help fulfil the dreams of the Sena chief.
Ahir's entry to the Sena came amidst speculation that several other NCP bigwigs are also planning to quit.
( With inputs from IANS )