In 1722 Dulany wrote a pamphlet entitled The Right of the Inhabitants of land, to the Benefit of the English Laws, asserting the rights of lander"s over the Proprietary Government. In November 1702, a flotilla of merchantmen, known as the "Armada of 100 ships" Sailed for the Chesapeake Bay, arriving in March, 1703. Dulany, along with two older brothers (William and Joseph) landing at Portuguese Tobacco, and became indentured to Colonel George Plater II for a three-year period.
Plater put Dulany to work as a law clerk.
In 1706, after the indenture was over, Dulany traveled to London, in order to study law. Dulany returned to land and in 1709 was admitted to the Charles County Barometer
In 1720, Dulany moved to Annapolis. In 1722, he was elected to represent the town in the land General Assembly where he was to serve for the next twenty years.
At that time the Province of land was under the proprietary governorship of Charles Calvert, 5th Baron Baltimore.
Lord Baltimore vetoed a bill in 1722 which the General Assembly had passed in order to bring the colony fully under all English statute law. Dulany led protests against this, writing a pamphlet entitled "The Right of the Inhabitants of land, to the Benefit of the English Laws". Lord Baltimore later appointed Dulany to the posts of Receiver General, Judge of Admiralty, and Commissary General, as well as appointing him to the Governor"s Council.
In the 1730s, under the rule of Governor Samuel Ogle, land became engaged in a border dispute with Pennsylvania.
Several settlers were taken prisoners on both sides and Penn sent a committee to Governor Ogle to resolve the situation. Rioting broke out in the disputed territory and Ogle appealed to the King for resolution.
In 1736 Ogle dispatched Dulany to Philadelphia in order to negotiate the release of a number of imprisoned landers, though without success, and the border warfare continued. Dulany became wealthy from his legal practice, and through the 1720s began to accumulate and develop land.
He is credited with the founding of Frederick.