"Their recent decision is not consistent with our values and so we have ended our sponsorship".
At the close of a trial at Belfast crown court in March a year ago, Jackson, his former teammate Stuart Olding and two of their friends were found not guilty of a series of sexual offences in relation to a party in Belfast in 2016.
In a statement released on Thursday, Diageo said: "We have met with the club to express our concerns".
"London irish has been open and honest with all of its sponsors, including offering to meet Diageo's senior management in Dublin in May, 2019".
Declan Kidney, who gave Jackson his worldwide debut as Ireland head coach, is the director of rugby at London Irish and had defended the club's signing of the outhalf.
That meeting has now resulted in the termination of the association Guinness have had with London Irish for nearly 30 years.
It is clear that the club anticipated a backlash over the signing and were prepared for it.
And the club last night said it was "understandably disappointed" by the Diageo decision and regretted the relationship had ended in such a manner.
This follows on from the news that another London Irish sponsor, Cash Converters, also cancelled their deal with the club over the controversial signing, earlier this week.
As a company, we are committed to the highest possible standards when it comes to our investments in any sponsorships and collaborations.
Cash Converters responded to a number of tweets about the club's decision to bring in the fly-half, saying it had decided- after a thorough review- to discontinue its association with the club.
The IRFU's decision to revoke Mr Jackson's contract was linked to social media and text messages revealed in the rape trial last April.
He is due to join London Irish from Perpignan where he played in the Top 14.
Their association started in 1992, but allegations that its parent company Diageo had "serious concerns" about Jackson joining the club for next season's Premiership campaign following a one-year stint in France have resulted in a parting of the ways.
The player was given his Ireland debut by Declan Kidney in 2013 and went on to win 25 global caps before his high-profile court case.