The woman, aged in her 20s, was spotted by officers monitoring the motorway's CCTV at around 7.25am.
Cameras showed a person dressed in black walking along the carriageway and crossing lives lanes, between J26 (Orrell Interchange, M58) and J25 (Bryn, A49).
The patrol room alerted Greater Manchester Police (GMP), who said it was also "called several times" by motorists alarmed by the person's erratic behaviour.
Initial reports suggested it was a man, but when patrols arrived at the scene, they found a woman with "welfare concerns".
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The force said it had to shut the road to deal with the incident because there is no hard shoulder on that stretch of the M6.
All traffic was brought to a halt whilst the woman was apprehended by officers and escorted to safety.
She has since been handed over to Merseyside Police, which has jurisdiction over the stretch of motorway near Wigan.
A police spokesman said: "Officers were called at about 7.25am today (August 2) over concerns for a woman walking south on the northbound M6 between junctions 26 and 25.
"A woman in her 20s was detained by police a short time later."
Both northbound and southbound traffic was held for around an hour before lanes reopened at 8.35am.
The incident led to northbound congestion back to J23 (Haydock) whilst traffic on the southbound carriageway was queued back to J27 (Standish).
Earlier this morning, North West Motorway Police tweeted: "There is a pedestrian on the M6 J26 to J27 Northbound. We are monitoring on CCTV and Police & Highways have been deployed.
"The male was running across both the northbound and Southbound c/way - Live lane. The traffic needed to be stopped for not just his safety but for road users."