A report by Congress’ nonpartisan research arm suggests U.S. Circuit Judge Merrick Garland would be a pragmatic voice if confirmed to the Supreme Court, scoring fewer ideological points and securing more victories than the outspoken conservative he would succeed, the late Justice Antonin Scalia.

The 78-page report from the Congressional Research Service, a branch of the Library of Congress, assessed Judge Garland’s record in 14 different areas of law, both for substance and scope. The report concluded “Judge Garland’s ability...