Leonard, 25 has been a target for Chris Wilder since last summer and whilst he has never given up the ghost in signing the want away midfield, the S2 club faced competition from Championship rivals Millwall for his signature.
Reports suggest that the Blades have finally agreed a fee with Southend, believed to be in-between £500-£700,000.
It isn't quite clear as to when he will team up with his new team mates but we anticipate him to feature in next Fridays Steel City showdown at home to Sheffield Wednesday.