He will join when he returns from holiday and becomes the Latics’ seventh summer signing.
Lincoln midfielder Butcher joins Oldham
The 24-year-old is just the latest player to exit the Imps following their play-off final defeat against Southend.
Eight more players including strike duo New Zealand-bound Simon Yeo, and Gary Taylor-Fletcher have already left Sincil Bank.
Taylor-Fletcher's agent has confirmed his client is wanted by at least four League One clubs.
Several others, including Peter Gain, Alan Marriott and Ben Futcher are tipped to follow suit, leaving Alexander with plenty of repair work to do ahead of the new season.