Mary Winchester has already died at the time the comic book prequel "Origins" begins. We can only know Mary Winchester through flashbacks and things her family knows about her.
Mary was born in 1954 and is the daughter of Samuel and Deanna Campbell, two demon hunters and has one brother named Jacob who is killed by a Hellhound, she is the wife of John Winchester.
Her eldest son is Dean Winchester and her youngest son is Sam Winchester.
Known friends: a woman named Julie who is killed while babysitting Dean and Sam.
When the angel, Castiel, sends Dean Winchester back in time (Season 4:3 - In The Beginning) it is discovered that Mary's family, the Campbells, are demon hunters going back generations. Mary comes to Azazel’s attention when she and her father Samuel interrupt him in the process of making a deal with a friend of hers. Mary’s beauty, intelligence, fighting ability and lack of fear gain Azazel’s admiration. In his quest to force Mary to willingly open her home to him Azazel kills her parents and then-boyfriend John Winchester, after which he bargains with Mary for John's life.
Mary accepts the deal, unknowingly setting off a chain reaction of events that lead to the apocalypse (Season 4:16 - All My Sins Remembered), and eventually marries John, leaving the life of a hunter completely and never revealing the true events surrounding her parents deaths. She gives birth to Dean on January 24, 1979, and Sam on May 2, 1983.
On November 2, 1983, Mary was awakened by sounds of six-month-old son Sam crying in his crib. Discovering an intruder there, she confronted him, realizing too late that it was Azazel, feeding baby Sam his blood, and that the deal she'd made had come due. A sleeping John was awoken by her screams, and finds Mary pinned to the ceiling with a large gash across her abdomen. She then burst into flames, igniting the rest of the house in the process.
Mary's spirit lingers to protect her children and when the boys return home to Lawrence, Kansas, for the first time in 20 years she apologizes for her past actions and then sacrifices the last of her essence to save them from a demonic spirit.