Mr. Peabody continued the practice of law in the city of New York, taking no active part in politics, but always observing with interest the course of events in the general government, and especially those connected with slavery and the slave power. He was an unconditional Whig, and his residence at the South in early life had given him such knowledge of slavery, in its effect on the slave, the owner, the free population, white and colored, and on general prosperity, that he early formed very positive opinions concerning it and its very great evils. On this, as on all other subjects, he was conservative and temperate in his opinions and feelings, taking no part in extravagant denunciations of those engaged in it, but always deprecating such courses as being, to his mind, not only inexpedient and unwise, but also unjust. With the strongest possible convictions against slavery on all grounds, moral and economic, he counseled moderation in the treatment of it. He was ever opposed to intemperate agitation, as tending to no good, but liable to lead to great evil. He was for years prior to the formation of the Republican party an active member of the Union Safety committee in New York, a body of conservative gentlemen of the highest character, organized to repress acrimonious treatment of the subject, as tending to alienate the different sections of the country, and to imperil the peace and possibly the integrity of the nation. When the Republican party was organized, adopting as its principles on the subject of slavery that it might remain undisturbed where it then existed, but should on no condition be extended into territory where it did not then exist, he accepted those views as the best terms for freedom to be obtained peaceably, and perhaps the best the lovers of freedom were warranted under the constitution in demanding. In 1855 he was a member of the convention which organized the Republican party of the state of New York. In the same year he was the candidate of the Republican party for election as justice of the supreme court of the state, to succeed Robert H. Morris, but his party was in the minority. In the same year (1855) he was appointed, by the governor of the state, justice of the supreme court, as the successor of Henry P. Edwards, deceased. In 1856 he was appointed justice of the supreme court of the state to fill a vacancy created by the resignation of James R. Whiting. In 1857 he was again the candidate of the Republican party for justice of the supreme court, but the party was not sufficiently strong to elect him. He served on the bench of the supreme court the terms for which he was appointed, and received more than the votes of his party at the times he was nominated for election.