He was chairman of the New Hampshire delegation in the Republican national convention at Chicago, in 1860, having been chosen a delegate at large by the state convention, with but a single vote in opposition. In the close contest between the friends of Lincoln and Seward in that convention, the New Hampshire delegation, under his lead, supported Lincoln from the first, and was strongly instrumental in securing his nomination. In 1861, Mr. Rollins was elected to congress from the second district, over the Democratic candidate, the late Chief-Justice Samuel D. Bell. He was re-elected in 1863, over Col. John H. George, and in 1865 over Hon. Lewis W. Clark, now associate justice of the supreme court. Mr. Rollins's congressional career covered the exciting period of the late civil war, and subsequent reconstruction, and he was throughout a zealous supporter of the most advanced Republican measures, such as the abolition of slavery in the District of Columbia, and the thirteenth and fourteenth amendments to the constitution, abolishing slavery throughout the Union, conferring citizenship and civil rights upon colored men, fixing the basis of representation in congress upon all citizens, without regard to color or previous condition, imposing political disabilities upon such civil and military officers of the government as had violated their oaths by engaging in the rebellion, declaring the inviolability of the public debt, and prohibiting forever the payment of that incurred in aid of insurrection or rebellion against the United States. To this entire policy Mr. Rollins gave a most earnest support, and took part zealously and efficiently in all the important legislation of those days. He was an industrious member of the committees to which he was assigned, serving on the committee on the District of Columbia, as chairman of the committee on Accounts, and a member of the committee on Public Expenditures, by which latter committee, during his service, a vast amount of labor was performed, especially in the investigation of the management of the New York and Boston custom-houses, involving the operations of the "blockade runners" during the war. He was also, on account of his well known parliamentary knowledge and skill, frequently called to the chair to preside over the house on turbulent occasions.