The Ravens (11-5) will play AFC East champion Miami, which eliminated the New York Jets 24-17 Sunday, in the first round of the playoffs.
McClain scored on runs of 5 and 1 yards. Willis McGahee ran 13 yards for another Baltimore score.
Joe Flacco completed 17-of-23 passes and Michael Clayton caught four passes for 128 yards for the Ravens.
David Garrard was 14-of-25 passing for 127 yards and a touchdown, with two interceptions, for the Jaguars (5-11).