They were among four new defensive players participating in team practice for the first time Saturday, joined by defensive tackles Justin Bannan and John Drew.
McIntosh played six seasons for the Washington Redskins before starting nine games for the St. Louis Rams in 2012. Mathis, a 2006 Pro Bowl selection, played all 10 of his NFL seasons in Jacksonville and holds the Jaguars' franchise interception record with 30.
Bannan is an 11-year veteran who started 15 games for the Denver Broncos last season and Drew was an undrafted rookie free agent out of North Carolina Central. The team announced the signing of the two defensive tackles on Friday.