Rajani is known for his expertise in the field for International Development work, particularly related to child rights, education, democracy, and open government in East Africa.

This work led to the formation of Twaweza in 2009, a program to promote access to information, citizen agency and better service delivery in Tanzania, Kenya and Uganda.

Through this Rajani played a key role in helping set up the Open Government Partnership, where he served as the civil society chairman for two years.

Another major program of the work started under Rajani's leadership is Africa's first nationally representative mobile phone survey, known as Sauti ya Wananchi (Citizen's Voices)[9] which regularly collects and publishes independent and scientifically credible data.

Rajani stepped down from Twaweza in December 2014 and became director of the Democratic Participation and Governance program at the Ford Foundation in New York, USA in January 2015, charged with strengthening the organization's global engagement.

[10] From 2014 until 2015, Rajani served on United Nations Secretary-General Ban Ki-moon's Independent Expert Advisory Group on the Data Revolution for Sustainable Development, co-chaired by Enrico Giovannini and Robin Li.