The deals for Whitehead and Gilchrist were two of several big player moves the Raiders made on Thursday during the league's free-agent period. Oakland also signed wide receiver Jordy Nelson, releasing receiver Michael Crabtree to make room for Nelson; signed running back Doug Martin and fullback Keith Smith; and finalized deals with blocking tight ends Derek Carrier and Lee Smith that had been agreed to earlier in the week.
Gilchrist joins the Raiders on a one-year deal after playing seven seasons with the Chargers, Jets and Houston. He has 11 interceptions, 32 passes defensed, 4 sacks, 5 forced fumbles and 2 fumble recoveries. He will likely step in as a starter alongside Karl Joseph.
The 29-year-old was cut by the Jets in May of last year after playing only two seasons with the team despite signing a four-year deal in 2015. Gilchrist tore his patellar tendon in Week 14 of the 2016 season and had major knee surgery that December.
Whitehead joins the Raiders after spending his first six seasons with Lions. He has 378 tackles, 3 sacks, 2 forced fumbles, 5 fumble recoveries, 4 interceptions and 18 passes defensed in 93 career games.
ESPN's Sarah Barshop contributed to this report.