In 1850, General Wilson was unanimously nominated for senator from Middlesex County by the free-soil and Democratic conventions, and elected by twenty-one hundred majority. When the legislature met, he was chosen President of the Senate. In 1851, he was reëlected and again chosen president. While President of the Senate, he was made Chairman of the Committee to welcome President Fillmore to Massachusetts, and also Chairman of the Committee to welcome Kossuth. In 1852, he was a delegate to the free-soil National Convention at Pittsburg, and was selected to preside over that body, and also made Chairman of the National Free-soil Committee. In the same year, he was unanimously nominated for Congress by the free-soilers of the eighth district, and, although the majority against the free-soilers in that district exceeded seventy-five hundred, he failed of an election by only ninety-three votes. A large portion of the free-soilers desired him that year to be a candidate for Governor, and most of the coalition Democrats likewise desired his nomination. In a public letter he peremptorily declined to be a candidate, notwithstanding which he received more than a third of the votes of the Free-soil State Convention at Lowell. In March, 1853, General Wilson was elected to the Constitutional Convention by the town of Berlin, and also by his own town of Natick. He was not absent from the convention for an hour during the session, and the journal and report of the debates show the active part taken by him in its transactions. During the temporary illness of the president, Mr. Banks, he was chosen president _pro tem_. In September, 1853, he was nominated by the Free Democratic State Convention, as candidate for the office of Governor. Out of six hundred votes cast by the convention, he received all but three. At the time he was nominated, men of all parties conceded the probability of his election. But the letter of Caleb Cushing, denouncing, in behalf of the administration, the coöperation of Democrats and free-soilers in State affairs--the bitter hostility of conservatism toward the new constitution, and the Irish vote against it--all contributed to overthrow the State reform party, and to defeat General Wilson and his friends.