During the New York Province royal governance of Lord Bellomont, Van Dam resisted his restrictions of commerce and Bellomont reacted confiscating some vessels of Van Dam, which would have infracted the laws of customs. By such struggle, Van Dam became engaged into politics. In 1699, Van Dam was elected to represent New York City into the New York State assembly, in Albany, and he became the opposition leader.
Van Dam rallied those merchants who had been affected by Bellomont's restrictions and together they issued a complain to the King of England, William III. Effectively, in response, the new royal governor Lord Cornbury removed some councilmen, in 1701, accusing them with promotion of political disorder. Into one of the vacancies of councilman, Van Dam was appointed instead, in 1702. Indeed, it was uncommon that a native of Albany became a royal governor councilman as it was an office which was usually reserved for prominent noble figures and wealthy New Yorkers. It functioned in New York city.
Van Dam served as a councilman for 30 years. As a councilman's rank was determined by the length of his tenure, eventually Van Dam reached the presidency of the council as the oldest member and, often, he represented the royal governor. For instance, Van Dam traveled annually to Albany, to renew the English-Iroquoian alliance on the governor's behalf.
After the royal governor John Montgomerie's death, Van Dam who was the council president was appointed temporary acting governor of New York Province, in 1731.
By opposing the Molasses act, Van Dam was rewarded, receiving 1,000 pounds by the assembly. Besides, the assembly had disposed a bill through which the liberal institutions of New York got much money. In April of 1732, the designated royal governor William Cosby arrived. Disliking such liberal maneuvers, Cosby decided that Van Dam should restore half of his salary of interim governor. Van Dam durst replying that, before he might comply for such demands, Cosby should return the privilege fortunes, which were being defalcated out of the English treasury for fake provincial expenditures, by Cosby since his appointment. Cosby assumed in August 1732 but Van Dam refused to take his corresponding oath of councilman.
Cosby was enraged by Van Dam's stubbornness so he filed a lawsuit against him to despoil the half of his acting governor salary. Van Dam was processed through a chancery court (with neither a jury nor a faithful following of the law texts) whereas his defense was taken by William Smith and James Alexander. The court of chancery was quite unpopular amongst the New Yorkers. Nonetheless, it was upheld although one of the three Supreme Court judges, the Chief Justice Lewis Morris, voted against it, in 1733, arguing the illegality of such type of chambers of justice. Despite his judicial victory, Cosby reacted so Van Dam was dimissed off the governor council and Morris was ousted. Nonetheless, Morris' liberal party won the elections in that same year, against the royal party.
In 1734, Van Dam's Heads of Articles of Complaint Against governor Cosby was published, at Boston, Massachusetts. Under the appellative of The Morrisites, the liberal party of New York aligned for Van Dam's claims, with his active participation. Oppositely, the royal loyalists, The Court Party, stood with Cosby.
John Peter Zenger's aggressively liberal New York Weekly Journal newspaper, of which Van Dam had been a founder (1733), used the Van Dam case much in its every day crusade of free government. Usually, like the other liberal figures of New York, Van Dam wrote unsigned articles which were published by Zenger. In 1734, Cosby burned piles of the publication, prosecuting Zenger in the historical Zenger's trial of 1735.
Usually, Van Dam was absent, off the regular sessions of the governor's council. By this reason, Van Dam was suspended by Cosby, who issued this secret order during his deathbed.
Thus, Van Dam didn't assume the New York governorship after Cosby's decease (1736). Instead, the corresponding councilman George Clarke, who was of the royal party actually, did. Van Dam demanded the office and, when Clarke refused, the two of them called for respective council sessions. Van Dam was supported by the Chief Justice James DeLancey and his adherents were ready to use the weapons to defend Van Dam's claim. Nonetheless, the conflict ended because, from London, several communiques endorsed Clarke's interim governorship.