A trade unionist and a social worker and also a Corporator at the Bombay Municipal Corporation, was one of the founding members of Hind Mazdoor Sabha. She was a long time member of M N Roy’s radical humanists and in the year 1929, formed the Sewa Mandir and worked in many slums and chawls especially those of the Bombay Improvement Trust. Her major political influence was under M N ROY and started her trade union work by taking active part in the activities of Bombay Municipal Workers Union. She was also part of the Girni Kamgar Union and during the anti colonial struggle she asked the workers to cut electric cables, disrupt railway lines and sent hundred of cables to the police force to join the workers. She won the municipal elections for the post of BMC Corporator from the D Ward in the year 1932. Later functioned as the president of the Hind Mazdoor Sabha and All India Railway Men's Federation and President of the Western Railways Employees Union during the 1960s.
A Sedition Case In the year 1932, Maniben Kara who was also a Corporator at the BMC and President of the Municipal Workers Union was charged under the Sedition on the basis of two speeches she made during the May Day programmes at Dongri Maidain. The Chief Presidency Magistrate convicted her under section 153(creating class hatred) and section 124 A9(sedition) and sentenced her to one year imprisonment and and a fine of Rs 300. She challenged the Magistrate order before the Bombay High Court through Advocate F S Talyarkhan. During the proceedings before the Bombay High Court her counsel raised the question whether the section related to promotion of class hatred could be applied in cases of employers and employees. The High Court judgement absolved her from the accusations and cancelled the imprisonment but continued with the fine. The judgement dwelt on length questions like Who is a Capitalist?
In 1950 she was booked along with M N Roy and V B Karnik under the Official Secrets Act for publishing a letter of the Ministry of Home Affairs in their publication Radical Humanist in which Maniben was the printer and publisher and Karnik the Editor but were later acquitted from the charges.
She died in the year 1979 and marking her first death anniversary, an institute by the name Maniban Kara Labour Institute was set up by the railway workers unions.