After serving a term in the Alabama legislature, he moved to Texas, where he opened a successful law practice.

In 1846, after Texas had become a state, Roberts was appointed district judge by Governor James Pinckney Henderson.

In January 1861 he was unanimously elected president of the Secession Convention in Austin, a meeting that he had been influential in calling.

Upon the ascension of the Democrats to power in Austin in 1874, Roberts was appointed by Governor Richard Coke to his former position of Chief Justice of the Texas Supreme Court.

He resigned as Chief Justice after receiving a unanimous nomination from the Democratic Convention to run for governor.

The present Capitol in Austin was contracted during Roberts's terms, and the cornerstone for the University of Texas was laid in 1882.

His impact on a generation of young attorneys was symbolized by the affectionate title "Old Alcalde" bestowed upon him by his students.

During his tenure at the university, Roberts wrote several professional works, among them a text, The Elements of Texas Pleading (1890), which was used for decades after his retirement from teaching.

In 1893, he left the university and moved to Marble Falls, where he turned his attention to more general historical writings.