Ashwani Saith has a fine biography of Ajit Singh for Ajit Singh (1940–2015), The Radical Cambridge Economist: Anti‐Imperialist Advocate Of Third World Industrialization for the latest issue of Development And Change.
The article highlights how his worldview and work was quite close to Nicky Kaldor.
Ajit Singh died on 23 June 2015 and there’s also a fine obituary on him in The Guardian by John Eatwell.
F.M. Scherer had a nice biography in the Palgrave Companion To Cambridge Economics.