The district can claim to have played a significant part in fostering the trade relations between Kerala and the outside world in the ancient and medieval period. It can also claim to have played an important part in fostering cultural relations and in laying the foundation of a cosmopolitan and composite culture in this part of the country. Kodungalloor which had the unique distinction of being the 'Premium Emporium India', also belongs to the signal honour or having first given shelter to all the three communities which have contributed to the prosperity of Malabar'. These three communities are the Christians, the Jews and the Muslims.

The history of Thrissur district from the 9th to the 12th centuries is the history of Kulasekharas of Mahodayapuram and the history since 12th century is the history of the rise and growth of Perumpadappu Swarupam. In the course of its long and chequered history, the Perumpadappu Swarupam had its capital at different places.

According to the literary works of the period, the Perumpadappu Swarupam had its headquarters at Mahodayapuyram and had a number of Naduvazhies in southern Kerala. Central Kerala recognised the supremacy of the Perumpadappu Moopil and he is even referred to as the 'Kerala Chakravarthi' in the 'Sivavilasam' and some other works.

One of the landmarks in the history of the Perumpadappu Swarupam is the foundation of a new era called Pudu Vaipu era. The Pudu Vaipu era is traditionally believed to have commenced from the date on which the island of Vypeen was thrown from the sea.

The 14th and 15th centuries constituted a period of aggressive wars in the course of which the Zamorins of Calicut acquired a large part of the present Thrissur district. In the subsequent centuries the Portuguese dominated the scene. By the beginning of the 17th century the Portuguese power in Kerala was on the verge of collapse.

About this time other European powers like the Dutch and the English appeared on the scene and challenged the Portuguese. Internal dissension in the Perumpadappu Swarupam helped the Dutch in getting a footing on the Kerala coast. As the Kerala chiefs were conscious of the impending doom of the Portuguese, they looked upon the Dutch as the rising power and extended a hearty welcome to them.

The decadence and consequential want of solidarity opened the flood gates of aggression. Hyder Ali and Tippu Sultan figured very prominently during the period. In 1790 Raja Rama Varma (1790-1805) popularly known as Sakthan Thampuran ascended the throne of Cochin. With the accession of this ruler the modern period in the history of Cochin and of the district begin. Sakthan Thampuran was the most powerful maharaja as the very name indicate. He is the architect of Thrissur town. Sakthan Thampuran ascended the throne just before the conclusion of a treaty with the English East Company. According to that treaty, Cochin threw off all allegiance to Tippu and became a tributary to the Company. The wave of nationalism and political consciousness which swept through the country since the early decades of this century had its repercussion in the district as well.

Even as early as 1919 a committee of the Indian National Congress was functioning in Thrissur. In the Civil Disobedience Movement of 1921, several persons in Thrissur town and other places in the district took active part and courted arrest. Thrissur district can claim the honour of having been in the forefront of the countrywide movement for temple entry and abolition of untouchability. The famous Guruvayur Satyagraha is a memorable episode in the history of the National Movement.

The Government of Cochin under the guidance of Sri. R. K. Shanmughom Chetti followed a policy of conciliation. By decree the public demand for the introduction of responsible Government in the State grew strong. In August 1938 Cochin announced a scheme for reforming the State legislature and introducing a system as per the Government of India Act of 1919 in the British Indian provinces. The administration of certain departments was entrusted to an elected member of the legislature to be nominated by the Maharaja. In the elections to the reformed legislature two political parties, viz. the Cochin State Congress and the Cochin Congress won 12 and 13 seats respectively. With the help of a few independents Ambat Sivarama Menon who was the leader of the Cochin Congress Party took up office as Minister under the scheme in June 1938. On his death in August 1938
Dr. A.R. Menon was appointed as Minister. When the State Legislature passed a vote of non-confidence against him, Dr. Menon resigned office on February 25,1942 and was succeeded by
Sri T.K. Nair who continued in office till July 11,1945.

The introduction of dyarchy did not satisfy the political aspirations of the people of Cochin. The idea of full responsible Government on the basis of adult franchise had caught their imagination. On January 26, 1941 a new political organisation called the Cochin State Praja Mandal took shape on the initiative of a few young politicians under the leadership of V.R. Krishnan Ezhuthachan.

The 'Quit India' Movement of 1942 had its echoes in the district. After the release of the leaders from jail in 1943, the Cochin State Praja Mandal pursued its organisational activities more vigorously. In the elections to the State Legislature in 1945 it won 12, of the 19 seats contested by its candidates. At the annual conference of the Praja Mandal held at Ernakulam in 1946 it was decided to start a state wide movement for the achievement of a responsible Government. The State Legislature was scheduled to meet on July 29, and it was decided that the day should be observed all over the State as 'Responsible Government Day'. In pursuance of this decision, meetings and demonstrations were held all over the State demanding the end of Dewan's rule and the transfer of full political power to the elected representatives of the people. The Maharaja of Cochin announced in August 1946 his decision to transfer all departments of the State Government except law and order and finance to the control of Ministers responsible to the State Legislature. In co-operation with other parties in the State Legislature, the Cochin State Praja Mandal decided to accept the offer. Consequently the first popular Cabinet of Cochin consisting of Panampilli Govinda Menon, C.R. Iyyunni, K. Ayyappan and T.K. Nair assumed office.

The first step towards the achievement of the goal of 'Aikyakerala' was taken with the integration of 'Travancore Cochin' States in July 1949. With the linguistic reorganisation of States in India, in November 1956 the Kerala State came into existence.