Maclean graduated in 1964 from Lawrence University with a B.A. Psychology. He received a law degree from the University of Denver College of Law in 1967. During the next few years he was a trial attorney for the Securities and Exchange Commission in Washington, D.C., an adjunct professor at Denver College of Law, magistrate in the Denver juvenile court, First Assistant Attorney General for the Colorado Department of Law, General Counsel of the Peace Corps. He was also an independent mediator and arbitrator.

His first book was In Broad Daylight , an account of the “vigilante killing” of town bully Ken Rex McElroy in downtown Skidmore, Missouri in 1981. 50 people, many of whom had gathered earlier in the day to figure out a way to handle the situation with McElroy if he got off on assault charges from an earlier incident, were said to have been on the street near where McElroy was shot with a high powered rifle and by a second assailant with a .22. However the prosecutor said he could not bring a case because no towns people would corroborate McElroy's wife's claim identifying the killer. In researching the book MacLean lived with a family outside the town for three years. “In Broad Daylight” won an Edgar Award for best true crime, was on the New York Times bestseller list for 12 weeks charting as high as 2, and was made into a movie starring Brian Dennehy. The book was reissued in 2007 with a new epilogue after the Nodaway County, Missouri prosecutor David Baird who had dealt with the case from the beginning released the county's investigation file..

MacLean's second book was Once Upon A Time, A True Story of Memory, Murder and the Law . Eileen Franklin, a California housewife, claimed to recover a repressed memory of her father murdering her playmate twenty years earlier in Foster City. Her father, George Franklin, was tried and convicted solely on the basis of the repressed memory. Franklin's conviction was later overturned by a federal court of appeals.

MacLean's most recent book, the Trial of James Ford Seale and Mississippi’s Struggle for Redemption chronicles the 2007 trial of James Ford Seale, for the murder of two black youths in southwest Mississippi in 1964. Seale was charged and convicted of torturing and drowning Charles Moore and Henry Dee in a backwater of the Mississippi River. The Past is Never Dead has recently been nominated for The William Saroyan International Prize for Writing, awarded by Stanford University Libraries.