In 1927 Gunawardena joined the League Against Imperialism in New York, where he worked with José Vasconcelos of Mexico, gaining a working knowledge of Spanish. In 1929 he went to London, where he participated in mass agitations and anti-colonial movements, excelling as a brilliant orator, trade unionist, and political columnist. Shri Jawaharlal Nehru and Krishna Menon of India, Jomo Kenyatta of Kenya, Tan Malaka of Indonesia, and Sir Seewoosagur Ramgoolam of Mauritius were some of his contemporary colleagues who later played prominent roles in their motherlands. He joined the staff of the new Daily Worker and took over the Workers' Welfare League of India, an organisation founded by Shapurji Saklatvala. He later crossed the channel to Europe and worked alongside socialist groups in France and Germany.
'T-Group'
In the midst of the Comintern's 'Left Turn', Gunawardena surreptitiously joined the Marxian Propaganda League of FA Ridley and Hansraj Aggarwala, who opposed the Stalinists' characterisation of the Social Democratic parties as social fascist. When Ridley and Aggarwala broke with Leon Trotsky, Gunawardena sided with the latter. In 1932 he travelled on the Orient Express to meet Trotsky at Prinkipo, but was stopped at Sofia by police. At the British conference of the League Against Imperialism, in May 1932, Gunawardena introduced a counter-resolution on India against those moved by Harry Pollitt. As a result, the Communist Party of Great Britain expelled him for Trotskyism.
Lanka Sama Samaja Party
However, he had gathered around him several like-minded Sri Lankans, including NM Perera, Colvin R de Silva and Leslie Goonewardene. They came to be known as the 'T-Group' – later forming the nucleus of the Trotskyist faction of the Lanka Sama Samaja Party. Scotland Yard, under orders from the India Office, thwarted him from his aim of going to India to build a new Communist Party there. He set out for the continent, meeting members of the Left Opposition in Paris. He then hiked over the Pyrenees to Barcelona, where he had a rare opportunity to meet the Trotskyists of Spainwho were soon to undergo a civil war.
Early political career in Sri Lanka and India
Soon after his return to Sri Lanka in November 1932, he plunged into active politics organising rural peasants, plantation workers and urban workers. He pioneered the founding of Lanka Sama Samaja Party in 1935. In 1936 he was elected to the State Council from Avissawella electorate where he continued his struggle for the betterment of workers and peasants. When World War II broke out Philip Gunawardena was detained on Governor's orders. However, in July 1942 he escaped to India and participated in the independence struggle there. In 1943 he was rearrested and detained in Mumbai, and after many months deported to Sri Lanka to be imprisoned till the end of war.
Post-war political career
On his release in 1945 he again started political and trade union activities. At the General Election in 1947 he was elected to the first Parliament to represent Avissawella seat, but soon he was unseated on his involvement in the General Strike in 1947, and lost his civic rights for seven years. He led the Viplavakari Lanka Sama Samaja Party since 1951 and as a constituent party formed the Mahajana Eksath Peramuna in 1956 under the leadership of Mr.SWRD Bandaranaike to form the first people's government in 1956 General Election. At that election, in 1956, he won the Avissawella seat with a large majority and served as a key member of the Cabinet of SWRD Bandaranaike as the Minister of Agriculture, Food, & Co-operatives. He is remembered as the architect of the Paddy Lands Bills which brought relief to the tenant cultivator and spearheaded the Port & Bus nationalisation, introduction of Multipurpose Co-operatives movement and establishing of the People's Bank, those brought tremendous change to society in Sri Lanka. In 1965, having won Avissawella from the MEP, Philip Gunawardena served in the National Government led by Dudley Senanayake, 1965–1970, as the Cabinet Minister of Industries and Fisheries. He established the Industrial Development Board, strengthened & expanded state industrial corporations and national private sector industries, and planned the development of the Fisheries sector.