Significant local political and religious changes occurred during his lifetime. In 1691, King and Queen County was created from New Kent County. Also, a new Anglican Parrish, St. Stephens, was established in that part of the county in which John Walker lived.

John was a captain in the militia and a justice of the county court. Until 1701 King William County was still a part of King and Queen County. Most of the land in the new county had been settled. John Walker was county sheriff in 1700-1702, a powerful and lucrative position. In his Virginia Colonial Abstracts, Beverley Fleet called John Walker "resolute" in exercising his duties. There was extensive political maneuvering in the colony during Walker’s tenure as sheriff. Virginia Governor Nicholson became enmeshed in a power struggle with a number of wealthy and influential Virginia landowners, many of whom held local political offices and were accustomed to handling affairs in their own jurisdictions themselves. Historian Robert Beverley, a large landowner and county clerk of King and Queen County at the time, was aligned with powerful opponents to the governor’s land policies and wanted the governor recalled for abuse of power. On a visit to London, Beverley, along with other distinguished Virginians, gave evidence against the Governor Nicholson to a committee sanctioned by Queen Anne to look into the accusations. One example of abuse Beverley cited was the governor’s treatment of John Walker, then sheriff of King and Queen County. The governor removed John Walker in the middle of his tax collection after he tried to collect several thousand pounds of tobacco (considered currency of the day) owed to the government by William Leigh, one of the governor’s political allies. This was particularly damaging to the sheriff because he was allowed a certain percentage of the tax revenue for making tax collections. In addition, John Walker would not pack juries for the governor nor would he hold enquires into levies and conversations of the governor's enemies in order to expose or ruin them, when there was no accusation, both of which were illegal. Nicholson was forced out of office in 1705. John Walker was elected sheriff again in 1706.

As sheriff John Walker received 2590 pounds of tobacco for the execution of the death sentence imposed on a Darby Colnon. Colnon had been tried in King and Queen and then sentenced by the General Court in Williamsburg for the murder of Jane Ford. Walker was reimbursed for transportation and lodging of the prisoner from King and Queen County to Williamsburg for sentencing and then back for execution, and for the rope to hang him.

As sheriff John Walker was required to give public notice for the directives of the Governing Council of Virginia. One was notice of a hearing in Williamsburg on a petition by Drammaco Chief Munguy, ruler of the Chicahominy Indians, on several matters relating to rights for the lands appointed to them. Attendance by persons pretending a right to any said lands was requested.

Besides his inheritance of Ryefileld, now Locust Grove, he was a large landowner in his own right. In 1687 he received a patent of 560 acres adjacent to the original patent of his father Thomas Walker while Thomas was still alive. The 1704 land tax list revealed that there were 383 landowners in the county, 26 of these owned 1000 or more acres. John owned 7000 acres. However, the acreage may not have been contiguous with the original Walker patent.

In 1701 there were 921 militiamen in King & Queen County. By 1707 John was a colonel in command of the militia and listed among the officers of King and Queen County his sons Capt. Thomas Walker, Lt. Richard Croshaw Walker and Cornet James Walker when he wrote to the Governor for advice engaging the Indians if they should attack. A traveler had conveyed that he had heard that well armed Indians were gathering in Maryland.

John Walker was interested in public affairs and served in the House of Burgesses where he brought issues forward for consideration. He referred to the colonial government a proposition to build a town on his land and in 1705 a charter for the town of Walkerton was granted. The House of Burgess passed a bill entitled “an act to enable the county of King and Queen County to purchase land to build a town” in 1705. John Walker deeded forty acres for use in establishing the town of Walkerton. Walkerton did not thrive as a town and in 1785 the bill was repealed and the land, except for the public road to/from the ferry across the Mattaponi, was returned to the Walker family.

He obtained permission to provide a safe haven for the French Huguenot refugees who were seeking to escape the religious persecutions that raged in France after the Revocation of the Edict of Nantes by Louis XIV. He received support in improving treatment of orphan children by having those in servitude treated in the same manner as indentured servants, by providing corn and clothes after their time of servitude expired. It appears he was interested in communications with the Indians because in 1707/8, he sent a list of Pamunkey words to the Governor.

He died after 1709 when William Byrd of Westover mentioned him in his diary, but before 1713 whe a petition to the court for settlement of a debt noted that he was deceased.