He wrote major opinions on the federal income tax, the Commerce Clause, and citizenship law, and he took part in important decisions about racial segregation and the liberty of contract.

Fuller's opinion in United States v. E. C. Knight Co. (1895) narrowly interpreted Congress's authority under the Commerce Clause, limiting the reach of the Sherman Act and making government prosecution of antitrust cases more difficult.

He argued in the Insular Cases that residents of the territories are entitled to constitutional rights, but he dissented when, in United States v. Wong Kim Ark (1898), the majority ruled in favor of birthright citizenship.

[2]: 7  He helped develop a gerrymandered system for congressional apportionment, and he joined his fellow Democrats in supporting provisions that prohibited African-Americans from voting or settling in the state.

[2]: 18 Public reaction to Fuller's nomination was mixed: Some newspapers lauded his character and professional career, while others criticized his comparative obscurity and his lack of experience in the federal government.

[7]: 116  They portrayed him as a Copperhead – an anti-war Northern Democrat – and published a tract claiming that "[t]he records of the Illinois legislature of 1863 are black with Mr. Fuller's unworthy and unpatriotic conduct".

[17]: 61  Justice Felix Frankfurter opined that Fuller was "not an opinion writer whom you read for literary enjoyment",[9]: 889  while the scholar G. Edward White characterized his style as "diffident and not altogether successful".

[21]: 1012  In what biographer Willard King calls "[p]erhaps the worst year in the history of the Court" – the term from October 1909 to May 1910 – two justices died and one became fully incapacitated; Fuller's weakened state compounded the problem.

[18]: 41  Summarizing Fuller's views of the law, scholar Irving Schiffman wrote in 1969 that "he was a conservative, laissez-faire Justice, less reactionary than some of his brethren, more compassionate than others, but a spokesman for what now seems a far-off and bygone judicial age".

[3]: 1481 According to legal scholar Bernard Schwartz, Fuller's most noteworthy decision was his 1895 opinion in Pollock v. Farmers' Loan & Trust Co.[23]: 184  In 1894, Congress passed the Wilson–Gorman Tariff Act, which contained a rider that levied a two-percent tax on incomes exceeding $4,000 a year.

[27]: 68  The decision provoked withering criticism from each of the four dissenters, including a paroxysm of ire by Justice John Marshall Harlan that one scholar characterized as "one of the most spectacular displays ever staged by a member of the Court".

[30]: 59  However, the Supreme Court has never formally overruled Pollock's reasoning; to the contrary, Chief Justice John Roberts cited it in the 2012 Affordable Care Act case National Federation of Independent Business v.

[25]: 813  Law professor Erik M. Jensen noted in 2014 that most legal academics agree that Pollock was "obviously dead wrong";[25]: 807  scholar Calvin H. Johnson called the decision "a terrible example of judicial bad behavior" that should be "reverse[d] in full".

[2]: 133–134  Citing Swift and other cases, legal historian James W. Ely has argued that Fuller was not opposed to federal antitrust laws per se, but only to expansive readings of the Commerce Clause.

[44]: 45  It proved a historically significant step toward expanding congressional authority, and legal scholar John Semonche wrote that by resisting it, Fuller "sought to put his finger in the dike".

[2]: 85  With Fuller's support, the Court in Allgeyer v. Louisiana (1897) unanimously expanded that component, concluding the Due Process Clause protected a right to enter into contracts.

[15]: 588–589  The opinion, written by Justice Rufus W. Peckham and joined by Fuller, maintained that the liberty protected by that clause included a right to enter labor contracts without being subject to unreasonable governmental regulation.

[49]: 109 Because of his support for property rights, Fuller favored a broad conception of the judicial role, endorsing doctrinal developments that expanded the federal courts' power to issue injunctions.

[54] Although some modern scholars have criticized the ruling in Young, attorney Rochelle Bobroff noted in 2009 that it "remains one of the most powerful tools to compel states to comply with federal law".

[27]: 231  His attorneys petitioned the Supreme Court for relief, arguing that racial bias had tainted the jury pool and that the threat of mob violence made the venue unfair.

[67]: 199 [68]: 96–97  In a 2021 book, Vernon Burton and Armand Derfner characterized Williams as one "of the most disgraceful decisions in Supreme Court history", writing it "abandoned Yick Wo" and "erased the Fifteenth Amendment".

[68]: 96–97 Fuller was among the seven justices who joined the majority opinion in Berea College v. Kentucky (1908),[37]: 129  a segregation case in which the Court refused to apply its freedom-of-contract principles in defense of racial equality.

[61]: 335, 337  In its challenge to the statute, Berea College cited Lochner and other similar cases to argue the law was "an arbitrary interference with the rights of the people in the conduct of their private business and in the pursuit of their ordinary occupations".

[69]: 732  The majority's reasoning stood in conspicuous conflict with its support for corporate rights in other contexts[2]: 159  and Donald Lively wrote the ruling "illuminated the evolving duality of Fourteenth Amendment standards".

[76]: 792  He contended that the Constitution could not tolerate unrestricted congressional power over the territories, writing that it rejected that proposition in a way "too plain and unambiguous to permit its meaning to be thus influenced".

[4]: 146  The Wong Kim Ark decision has taken on additional significance as prominent Republican politicians, including Donald Trump, have called for the reversal of birthright citizenship.

[18]: 37  Asserting that its justices "ignored the Fundamental Law", Princeton professor Alpheus T. Mason argued that "[t]he tribunal Fuller headed was a body dominated by fear—the fear of populists, of socialists, and communists, of numbers, majorities and democracy".

[80]: 3  In a 1998 review of Ely's book, law professor John Cary Sims argued that Fuller and his fellow justices failed to fulfill their obligation to go "against the prevailing political winds" instead of simply deferring to the majority.

[91]: 102–03  George Skouras, writing in 2011, rejected the ideas of Ely, Ackerman, and Gillman, agreeing instead with the Progressive argument that the Fuller Court favored corporations over vulnerable Americans.

[101] County commissioners accepted the offer later that month; they agreed that the statue could remain in front of the courthouse for up to a year while the original donor attempted to find a new location where it can be displayed.