The man, in his 30s, from the Stafford area, fell from the Aston Bank bridge, near to the Doxey work site, onto the M6 southbound between Junctions 14 and 13, yesterday just after 2.45pm.
He was taken to Royal Stoke University Hospital where he remains in critical but stable condition.
Two lanes were closed for more than two hours while officers carried out an investigation at the scene.
Jordan Eggington, spokeswoman for West Midlands Ambulance Service, said: "We were called at 2.47pm yesterday to the southbound carriageway of the M6 between junctions 14 and 13.
"An ambulance, a paramedic officer, the Midlands Air Ambulance from Tatenhill and a North Staffordshire BASICS doctor attended the scene.
"On arrival, crews found a man in a critical condition after falling from height. Staff administered advanced trauma care on scene before conveying the man to Royal Stoke University Hospital on blue lights and sirens.”
Any witnesses or anyone with relevant dashcam footage is asked to get in touch by either messaging Staffordshire Police on Facebook or Twitter, calling 101 quoting incident number 398 of 30 July or by emailing the investigation team direct at firstname.lastname@example.org.
Help and advice for those having a mental health crisis is available from a number of agencies.
Samaritans - 116 123 or samaritans.org
Access Service for Adult Mental Health - 03001 240365
Every Mind Matters - nhs.uk/oneyou/every-mind-matters