When Ceylon received independence and dominion status in 1948, Colonel Kotelawala contested the 1947 general elections from the United National Party (UNP) founded by D. S. Senanayake from the Dodangaslanda electorate and was elected to the newly formed House of Representatives, which was the elected lower house of parliament established under to Soulbury Constitution.
Kotelawala was an important member the UNP and was appointed by Senanayake as Minister of Transport and Works, retaining the portfolio of public works which he had held in the second board of ministers.

During his tenure major projects such as the Laxapana power project, expansion of the Colombo harbor, expansion of the Ratmalana Airport, construction of the University of Peradeniya and the expansion of road in the island took place.
With S. W. R. D. Bandaranaike leaving the UNP and crossing over to the opposition, Kotelawala was appointed Leader of the House in the House of Representatives on 12 July 1951.

When Senanayake suddenly died on 22 March 1952, Kotelawala expected to succeed him as Prime Minister, given he was the leader of the house and the most senior member of the UNP.
However, to much of his anger, Lord Soulbury, the Governor-General appointed Senanayake's son and Kotelawala's younger cousin, Dudley Senanayake as Prime Minister on 26 March 1952.
An angry Kotelawala threatened resignation and a possible split in the party appeared.
After mediation between Kotelawala and Senanayake by senior UNP members including Sir Oliver Goonetilleke, Kotelawala agreed to serve in Dudley Senanayake's cabinet retaining his existing portfolio.
Soon after Senanayake called for fresh elections and in the 1952 general elections Kotelawala was re-elected and retained his ministry and the post of leader of the house as the UNP won a majority to form a government.

The following year, the Senanayake government faced a major civil unrest with left-wing parties launching the 1953 Hartal in August.
On 12 August 1953 civil disobedience, strikes and demonstrations started through out the island by trade unions against the proposed elimination of the subsidy on rice by the government.
The country came to standstill with transport and communication stopping due to acts of sabotage.
The government implemented emergency regulations and deployed the army to suppress the Hartal and restore order.
Badly shaken by the events of the Hartal, Senanayake gravely ill resigned as Prime Minister on 12 October 1953.
Kotelawala succeeded Senanayake as Prime Minister; Minister of Defense and External Affairs; and leader of the UNP.
When Ceylon received independence and dominion status in 1948, Colonel Kotelawala contested the 1947 general elections from the United National Party (UNP) founded by D. S. Senanayake from the Dodangaslanda electorate and was elected to the newly formed House of Representatives, which was the elected lower house of parliament established under to Soulbury Constitution. Kotelawala was an important member the UNP and was appointed by Senanayake as Minister of Transport and Works, retaining the portfolio of public works which he had held in the second board of ministers.
During his tenure major projects such as the Laxapana power project, expansion of the Colombo harbor, expansion of the Ratmalana Airport, construction of the University of Peradeniya and the expansion of road in the island took place. With S. W. R. D. Bandaranaike leaving the UNP and crossing over to the opposition, Kotelawala was appointed Leader of the House in the House of Representatives on 12 July 1951.
When Senanayake suddenly died on 22 March 1952, Kotelawala expected to succeed him as Prime Minister, given he was the leader of the house and the most senior member of the UNP. However, to much of his anger, Lord Soulbury, the Governor-General appointed Senanayake's son and Kotelawala's younger cousin, Dudley Senanayake as Prime Minister on 26 March 1952. An angry Kotelawala threatened resignation and a possible split in the party appeared. After mediation between Kotelawala and Senanayake by senior UNP members including Sir Oliver Goonetilleke, Kotelawala agreed to serve in Dudley Senanayake's cabinet retaining his existing portfolio. Soon after Senanayake called for fresh elections and in the 1952 general elections Kotelawala was re-elected and retained his ministry and the post of leader of the house as the UNP won a majority to form a government.
The following year, the Senanayake government faced a major civil unrest with left-wing parties launching the 1953 Hartal in August. On 12 August 1953 civil disobedience, strikes and demonstrations started through out the island by trade unions against the proposed elimination of the subsidy on rice by the government. The country came to standstill with transport and communication stopping due to acts of sabotage. The government implemented emergency regulations and deployed the army to suppress the Hartal and restore order. Badly shaken by the events of the Hartal, Senanayake gravely ill resigned as Prime Minister on 12 October 1953. Kotelawala succeeded Senanayake as Prime Minister; Minister of Defense and External Affairs; and leader of the UNP.
John Kotelawala