In Pune, Modak came in touch with Dr. Jabbar Patel and Satish Alekar, who were directoing various plays and trying to provide a new dimention to Marathi theatre. He started his music career in 1972, assisting Bhaskar Chandavarkar, the composer for Vijay Tendulkar's noted play "Ghashiram Kotwal" directed by Dr. Jabbar Patel in Pune. Later Anandji started composing independently in 1974, with Satish Alekar's acclaimed Marathi play "Mahanirvan" for Theatre Academy, Pune, a theatre organisation in 1973 he was also one of the founder members of the academy.
Meanwhile, he worked with Bank of Maharashtra while still composing music, he completed his 35 years service & retired from job in 2010. His started working with theatre and eventually started composing music for radio, television, plays and Marathi cinema. He also composed music for devotional, semi-clasical, classical and pop music. He was known for his experimental style, and very effecitve music with minimum instruments.
His most notable work involves award winning movies like "Chaukat Raja", "Tu Tithe Mee" and "Harishchandrachi Factory", "Mukta" and plays like Mahapur, Kheliya, Raigadala Jeva Jag Yete, Begum Barve, Vitthala, Tumche Aamche Gane. One of his last films was biopic "Yashwantrao Chavan – Bakhar Eka Vadalachi" (2014). Over the years, he received popular and critical acclaims for his work. He won Maharashtra State Film Award for Best Music, for Kalat Nakalat, Raju, Doghi, Mukta, Raosaheb, and Dhoosar. Till date he is the only music director in Marathi film industry who won 6 Maharashtra State Film Award for Best Music category.
His finest musical work came perhaps in Marathi non-film category. In 1980s and 1990s he was part of a prolific group in Pune whose other prominent members were Chandrakant Kale, Madhuri Purandare, Rajeev Paranjape. They did much acclaimed shows like Preet-rang and Amrit-Gatha; for Amrut-gatha, Anand Modak had set to tune verses of saints Jnandev, Namdev, Eknath, Tukaram.