Leaving office in 1843, he passed the next six years in professional labors, varied by occasional addresses of a literary or patriotic cast, and by many Whig speeches in the campaigns of 1844 and 1848. To his practice in the State courts was united that in patent cases, which not only brought him a lucrative clientage, but largely increased his acquaintance with public men at Washington. His gubernatorial service had given him national fame, and he was, although not in public life, esteemed as one of the national leaders of his party. In the courts he commanded respect for the clearness and strength of his arguments, but, even there, he was at his best when his heart inspired his speech with fervor, as in his pleas for Van Zandt and others charged with harboring fugitive slaves. The defence of Greeley, in the Cooper libel suit, and of the Michigan rioters, may be cited as instances of his persuasiveness before juries, but that in the case of William Freeman is celebrated both for its own quality and the intrepidity of its author. Gladstone has characterized it as the greatest forensic effort in the English language, not excluding the masterpieces of Erskine. It is a plea for the life of a brutalized negro who butchered a whole family under circumstances of peculiar atrocity. The deed was without excuse or palliation, save in the insanity of the perpetrator, of which Seward became convinced, and volunteered as counsel amid the surprise, imprecations, and threats of the Auburn community, where the case was at issue. The moment was a supreme one for him, but he did not hesitate. Without reward, or the hope of reward, even in the gratitude of the insensate wretch for whom he risked professional standing and public favor, he worked as indefatigably as though the weightiest honors and emoluments depended thereon, from the impanelling of the jury to the failure of executive clemency; but Freeman's death in prison and the autopsy that disclosed the morbid condition of his brain fully vindicated Seward's analysis and exalted him in public regard.