He participated in the battle of San Jacinto in William H. Smith's cavalry company, his name appearing on the original muster roll, through error, as W.W. Williamson. He received 640 acres for participating in the battle of San Jacinto. On December 16, 1836, the First Congress of the republic elected Williamson judge of the Third Judicial District, automatically making him a member of the Supreme Court. The town of Columbus had been burned during the Runaway Scrape, and as there was no suitable structure to hold court proceedings, the first term of District Court, Republic of Texas, was convened by the Honorable R.M. Williamson, under a large oak tree next to the lot where the Colorado County Courthouse was later built in April 1837. In 1840 he was elected to represent Washington County in Congress. He served in the House in the Fifth, Sixth, and Seventh Congress, in the Senate in the Eighth Congress, and in the House again in the Ninth Congress. His Senate seat in the Eighth Congress was contested, and he eventually lost the seat. After annexation, which he had advocated so strongly that he even named one of his sons Annexus, he served in the Senate of the first two legislatures, retiring in March 1850.
As judge and lawmaker Williamson became the subject of numerous legends inspired by his personal characteristics, his unique decisions, his adroitness as a campaigner, his amusing legislative manipulations, and the succinctness of his oratory. Williamson married Mary Jane Edwards, daughter of Gustavus E. Edwards of Austin County, on April 21, 1837. They were parents of seven children. After his defeat in the race for Congress in 1850, he retired to his farm near Independence and devoted himself to the education of his children and preparations of materials for writing a history of events in Texas leading up to the Texas Revolution. He was an unsuccessful candidate for lieutenant governor in 1851. In 1857 an attack of illness affected his mental brilliance, which was further impaired by the death of his wife in 1858. From these combined shocks his mind never entirely recovered. He died at the home of his father-in-law in Wharton on December 22, 1859. Williamson County, established in 1848, was named for R. M. Williamson. In 1930, when his body was reinterred in the State Cemetery, the state of Texas erected a monument at his grave. The Texas Centennial Commission, in 1936, marked the site where he died.
30° 15.933, -097° 43.632
Texas State Cemetery