Kartini studied at universities in both Surabaya and Yogyakarta before moving to Jakarta where she majored in the Faculty of Law and Social Sciences at the University of Indonesia, gaining her law degree in 1958. She became a judge in the Jakarta special court, one of the first Indonesian judges after the formerly purely Dutch justice service was replaced with an indigenous one.

At the death of her husband in 1973, Kartini resigned, needing a larger income to support her and her family than the judiciary could provide. She started work as a notary, eventually setting up her own attorney and legal consultant office Kartini Muljadi & Rekan (KMR).

Together with her children, and with help from the contacts she made through her law practice, she founded the Tempo Group, which included the medicine and consumer goods manufacturer PT Tempo Scan Pacific.