Romney, now a U.S. senator from Utah and an off-and-on Trump critic, was responding to the report by Special Counsel Robert Mueller, who described how Trump sought to disrupt the probe into ties between his presidential campaign and Russia.
Mueller did not establish that Trump's campaign team colluded with Moscow and he did not charge the president with obstructing justice, but the report provided extensive details of Trump's efforts to thwart the probe.
Romney said it was "good news" that there had been insufficient evidence to charge Trump with conspiring with a foreign adversary or obstructing justice, which he said could have triggered a constitutional crisis.
"Even so, I am sickened at the extent and pervasiveness of dishonesty and misdirection by individuals in the highest office of the land, including the President," Romney said in a statement posted on Twitter.
"I am also appalled that, among other things, fellow citizens working in a campaign for president welcomed help from Russia - including information that had been illegally obtained; that none of them acted to inform American law enforcement; and that the campaign chairman was actively promoting Russian interests in Ukraine," he added.
Romney was sharply critical of Trump during the 2016 presidential campaign before being considered briefly as a candidate for secretary of state in Trump's administration.
His sharp statement on Friday breaks with the position of other Republicans and the White House, which has declared the report a victory for the president.
Trump has repeatedly dubbed the investigation a "witch hunt" and insisted he did not engage in collusion or obstruction.
Trump remains popular with most Republicans but a potential challenge from someone such as Romney in the Republican primary process next year could complicate Trump's bid to win a second term in 2020.
Romney lost the 2012 presidential election to Democratic candidate Barack Obama.
Congressional Democrats on Friday took legal action to get hold of all of Mueller's evidence from his inquiry.