His mother died before his first birthday and his stepmother the next year. From 1910 onwards he was in the custody of his maternal grandmother Parvathiammal in the neighbouring village of Kallupatti. Parvathiammal was furious on Thevar's father for having taken two new wives shortly after the death of his second wife.
During his youth, Thevar was aided by Kuzhanthaisami Pillai. Pillai was a close family friend of Thevar's father. Pillai took responsibility for arranging Thevar's schooling. First he was given private tuition and in June 1917 he began attending classes at an elementary school run by American missionaries in Kamuthi. Later he joined the Pasumalai High School(near Thirupparankundaram) and then he shifted to the Union Christian High School in Madurai.
Thevar would however, not complete his studies. In 1924 he missed his final examinations due to an outbreak of a plague epidemic. The following year he also missed his chance to attend the final examinations, as he returned to Pasumpon to fight a legal battle over issues of inheritance of family property. The case would linger and was not settled until 1927, when the court ruling in Muthuramalingam Thevar's favour.
Thevar's father, Ukkirapandi Thevar, died on June 6, 1939.
Following his return from Calcutta, Thevar began to study religious spiritualism, Tamil language and classical literature. He was strongly influenced by thinkers such as Swami Vivekananda and Savant Ramlinga Adigal. He began to adopt a simple and strict lifestyle, as well as interacting all castes in the local communities.
As an apprentice of S. Srinivasa Iyengar, Thevar was increasingly involved in the political activities of the Indian National Congress. He was active in the civil disobedience movement called by Gandhi, and acted as a courier between 1932-1934. Moreover he led temperance campaigns in Kallupatti, Mudukulathur and Kodhumazhur. His activities angered the colonial authorities, and he was jailed on several occasions.
In 1934 Thevar organised a convention at Abhiram, which urged the authorities to repeal the CTA. A committee consisting of Thevar, Dr. P. Varadarajulu Naidu, Perumal Thevar, Sasivarna Thevar and Navaneethakrishna Thevar was appointed by the convention to carry on the efforts to persuade the government to revoke the Act.
The CTA was, however, not revoked. On the contrary, its implementation was widened. Thevar again led agitations and awareness-raising campaigns against the Act. At the time the Justice Party was governing the Madras presidency, and their refusal to revoke the law created a strong animosity on Thevar's behalf towards the Justicites.
After the election Thevar made a bid to be elected the president of the District Board. So did P.S. Kumarasamy, the Raja of Rajapalyam. Conflict erupted within the local Congress organisation over the issue. S. Satyamurthi, on behalf of the Tamil Nadu Congress Committee, intervened to preserve the unity of the Congress. Thevar was convinced to withdraw his candidature for president, and presented a motion nominating Kumarasamy as president.
When the Congress Socialist Party began to mobilize in the Madras Presidency in 1936, Thevar joined their ranks.
In February 1937 Thevar contested the assembly election himself, as a candidate in the Ramathapuram constituency. He had a powerful opponent, the Raja of Ramnad. However, Thevar won a landslide victory with 11 942 votes against 6 057 for the Raja.
Following the election the Congress formed a government in the Presidency. Thevar had high hopes that the new Congress ministry would revoke the Criminal Tribes Act. But the new Chief minister, C. Rajagopalachari, did not fulfil those hopes.
In 1945, he would become the founding president of the TVS Thozhaili Sangam.
However, due to the manoeuvrings of the Gandhi-led clique in the Congress Working Committee, Bose found himself forced to resign from the Congress Presidency. He then launched the Forward Bloc on June 22, calling for the unification of all leftwing elements into a united organisation within the Congress. Thevar, who was disillusioned by the official Congress leadership which had not revoked the CTA, joined the Forward Bloc. When Bose visited Madurai on September 6, Thevar organised a massive rally as his reception.
Elections to the assembly of the Madras Presidency were again held in March 1946. Thevar contested from the Mudukulathur constituency, and was elected unopposed. Soon thereafter, the CTA was repealed.
In February 1948 the Congress expelled all dissenting fractions, including the Forward Bloc. The Forward Bloc became an independent opposition party, and Thevar became its president of its Tamil Nadu state unit (a position he would hold for the rest of his life).
On January 23, 1949, in connection with birthday anniversary celebrations of Subhas Chandra Bose, Thevar publicly announced that Bose was alive and that he had met him. Soon thereafter Thevar disappeared without any explanation. He returned to public life in October 1950. Rumours claimed that he had travelled to Korea and China during this period.
On the national level the Forward Bloc had been suffering from internal ideological divisions. In 1948 two separate Forward Blocs had emerged, a 'Forward Bloc (Marxist)' (out of which the Forward Bloc of today emerged) and a 'Forward Bloc (Ruiker)' (led by R.S. Ruiker). On June 23, 1951, the two parties reunified at a meeting in Calcutta. A central committee was announced for the united party, which included Thevar as one of its members.
After the election, Congress lacked a majority of its own in the Madras legislative assembly. Thevar cooperated with the communists in trying to form a non-Congress governing coalition. However, the governor intervened and made C. Rajagopalachari of the Congress the Chief Minister.
An extraordinary central committee meeting was convened in Nagpur May 11-15, 1955. Singh, Yagee and their followers were expelled from the party. Hemanth Kumar Bose was elected chairman of the party, Haldulkar the general secretary and Thevar the deputy chairman of the party. Thevar would hold that post until his death.
A new dynamic in the efforts to build a non-Congress front had emerged in the Madras State(which had been reorganised in 1956). The Congress had been divided and C. Rajagopalachari had formed a new party, the Congress Reform Committee (CRC). Thevar now made peace with his former enemy C. Rajagopalachari, and the Forward Bloc and the CRC worked together to defeat Kamaraj and the Congress rule in the state.
In the election Thevar again contested both the Aruppukottai constituency in the Lok Sabha election and the Mudukulathur constituency in the assembly election. He won both seats, but this time he decided to vacate the assembly seat.
Thevar himself travelled to Delhi on July 17 to attend the session of the Lok Sabha. He returned on September 9. On September 10 he took part in a 'Peace Conference' together with D.V. Sasivarna Thevar and Velu (a Dalit legislative assembly member of the Forward Bloc). From the Congress side six Dalits took part. There was also a delegate from the Nadar caste. The conference concluded that the three castes should live in harmony.
Emmanuel, the leader of the Congress Dalits at the Peace Conference was killed the following day. On September 28, a few days after the clashes had ceased, Thevar was arrested by the police under the Preventive Detention Act. Thevar's was apprehended directly after holding a speech at the conference of the Indian National Democratic Congress (the new name taken by the Congress Reform Committee). Thevar was taken to the Jail. Pudukkottai court was hearing that case. He was later accused of having masterminded the murder of Emmanuel.
The Forward Bloc and its allies condemned Thevar's arrest as a political vendetta, engineered by the Congress. A 'Thevar Committee' was step up by the INDC. Thevar was acquitted of all charges and released in January 1959.
Following the election, Thevar health deteriorated and he largely withdrew from public life. He was nominated for the 1962 Lok Sabha election. However he only attended a single campaign meeting, which also was attended by C. Rajagopalachari (who now had merged with his INDC with the Swatantra Party). Thevar was reelected, but due to health reasons he was unable to travel to the parliament in Delhi. U. Muthuralingam Thevar died on October 30, 1963, on his 55th birthday.A bye-election for the Aruppukottai Lok Sabha constituency seat vacated by his death was held in 1964, in which the Forward Bloc was defeated for the first time.
As an Indian nationalist, Thevar condemned the Dravidar Kazhagam its successor DMK for stimulating separatism and parochialism. Moreover he distrusted the Atheist element of the Dravidian political discourse.
After his death, the Forward Bloc entered into a period of decline in Tamil Nadu. The party leadership was overtaken by Thevar's disciple P.K. Mookiah Thevar. The party organisation became ridden by splits and disputes. In this situation, the major chunk of the Maravar vote-bank of the Forward Bloc was overtaken by the Dravida Munnetra Kazhagam and the All India Anna Dravida Munnetra Kazhagam.
Several official honours have been given to Thevar. In 1968 the Pasumpon Muthuramalinga Thevar College was founded in Usilampatti by the then DMK-led state government. His biography was included in the high school textbooks in Tamil Nadu. In 1971 his cemetery in Pasumpon was converted into an official memorial. A life-size portrait of Thevar was installed in the Tamil Nadu assembly in 1980. In 1984, after the bifurcation of the Ramnad District the 'Pasumpon Muthuramalingam District' was created. Greenways Road and Chamiers Road, two important arterial roads in Chennai, were renamed after Thevar, and currently there is a statue of Thevar where his eponymous road intersects with Anna Salai.
U. Muthuramalingam Thevar is revered as a hero of the Thevar/Maravar community. Thevar was become an icon in the political life in southern Tamil Nadu. Many political parties seeking the support from that community at the time of elections will make pay their respect to him. But at the same time his legacy is not entirely uncontroversial. At times violence between Thevars and Dalits flare up in the area, and desecrations of monuments of Thevar have taken place.