I found this run-down over at Lawfare (agnostic on the merits, but rightfully harsh about Trump’s public dumping on McCabe) helpful, especially this section on the professionals who recommended his dismissal:
The FBI takes telling the truth extremely seriously: “lack of candor” from employees is a fireable offense—and people are fired for it. Moreover, it doesn’t take an outright lie to be dismissed. In one case, the bureau fired an agent after he initially gave an ambiguous statement to investigators as to how many times he had picked up his daughter from daycare in an FBI vehicle. The U.S. Court of Appeals for the Federal Circuit ruled against the agent when he appealed, finding that “lack of candor is established by showing that the FBI agent did not ‘respond fully and truthfully’ to the questions he was asked.”
Consider also that although Sessions made the ultimate call to fire McCabe, the public record shows that the process resulting in the FBI deputy director’s dismissal involved career Justice Department and FBI officials—rather than political appointees selected by President Trump—at crucial points along the way. To begin with, the charges against McCabe arose out of the broader Justice Department Office of Inspector General (OIG) investigation into the FBI’s handling of the Clinton email investigation. While the inspector general is appointed by the president, the current head of that office, Michael Horowitz, was appointed by President Barack Obama and is himself a former career Justice Department lawyer. As Jack Goldsmith has written, the inspector general has a great deal of statutory independence, which Horowitz has not hesitated to use: Most notably, he produced a highly critical 2012 report into the Justice Department’s “Fast and Furious” program. So a process that begins with Horowitz and his office carries a presumption of fairness and independence.
After investigating McCabe, Horowitz’s office provided a report on McCabe’s conduct to the FBI’s Office of Professional Responsibility (OPR), which investigates allegations of misconduct against bureau employees. This office is headed by career Justice Department official Candace Will, whom then-FBI Director Robert Mueller appointed to lead the OPR in 2004. According to Sessions, the Office of Professional Responsibility agreed with Horowitz’s assessment that McCabe “lacked candor” in speaking to internal investigators.
Finally, Sessions’s statement references “the recommendation of the Department’s senior career official” in advocating McCabe’s firing on the basis of the OIG and OPR determinations. (The official in question appears to be Associate Deputy Attorney General Scott Schools.)
So while Sessions made the decision to dismiss McCabe, career officials or otherwise independent actors were involved in conducting the investigation into the deputy director and recommending his dismissal on multiple levels.