At Starfleet Medical in 2151, Williams was part of a group of Starfleet officers who conferred with Vulcan Ambassador Soval regarding the disposition of Klaang, a Klingon courier who had recently crash landed on Earth. Along with Jonathan Archer, Williams objected to the Vulcans attempting to subvert the decision-making process from Starfleet. (ENT: "Broken Bow")
In 2152, Williams joined Admiral Forrest in defending Captain Archer's actions when Soval accused Archer of disobeying direct orders and failing to deliver Sub-Commander T'Pol to the Vulcan ship D'kyr. When Soval suggested that T'Pol was not accompanying Archer of her own free will, Williams angrily insisted that Archer was not "in the habit of kidnapping Vulcans." (ENT: "Shockwave, Part II")
In 2153, Williams placed a bet with an archaeologist named Drake as to the existence of a crashed spacecraft in the Arctic Circle, promising to provide Drake with a bottle of scotch if such a debris field were to be found. Although Drake and his team ultimately discovered the field, they were assimilated by the survivors and turned into cybernetic hybrids controlled by a hive mind. After three days of no contact with the team, Commander Williams and Admiral Forrest traveled to the excavation site, only to find no evidence of any Humans. Forrest subsequently issued orders to Captain Archer to initiate a pursuit of the team's vessel, which had been taken over by the aliens. (ENT: "Regeneration")
Along with the Command Council, Williams was involved in Archer's debriefing after Enterprise returned from the Delphic Expanse in 2154. Upon the conclusion of the proceedings, Williams relayed the Council's orders that all details of the debriefing were to remain classified. (ENT: "Home")
Williams was played by actor Jim Fitzpatrick.
He was named after William Shatner, the Star Trek: The Original Series actor who played James T. Kirk. In a character breakdown sheet that Paramount sent to talent agents when trying to find a suitable actor for the part, Commander Williams was stated to be a non-recurring role and was described thus; "Human male. 50s. A somewhat temperamental Starfleet officer who serves as attaché to Admiral Forrest." 
His first name was given as "Marcus" in A Choice of Futures. The novel also introduces his daughter Valeria, a Starfleet lieutenant, who is implied to be developing a romance with a crewmate, Samuel Abraham Kirk, with the hint that they are the future parents of Tiberius Kirk, and thus the great-grandparents of James T. Kirk. This would also mean that Commander Williams is a direct ancestor of the character whose portrayer he was named for.