Final answer:
The formal name of the legislative body in which 'Tryst with Destiny' was first delivered is Constituent Assembly of India. Jawaharlal Nehru delivered this speech on August 14, 1947, marking the independence of India from British colonial rule.
Step-by-step explanation:
The formal name of the legislative body in which 'Tryst with Destiny' was first delivered is Constituent Assembly of India. This historic speech, delivered by the first Prime Minister of India, Jawaharlal Nehru, on August 14, 1947, marked the independence of India from British colonial rule. The Constituent Assembly of India was responsible for drafting the Constitution of India, which came into effect on January 26, 1950.