Mr Mitchell and former Tennis Australia president Steven Healy were accused by the Australian Securities and Investments Commission of breaching their duties as directors by favouring Seven during the negotiations in 2012 and 2013 for the five-year rights deal to broadcast the Australian Open.
The corporate watchdog alleged Mr Mitchell and Mr Healy withheld material from the Tennis Australia board during the negotiations;did not tell the board of the value of the rights;and failed to highlight the interest of other bidders,notably Network 10 and US group IMG.
The trial,which ran over three weeks late last year,saw a who's who of the media world take to the witness box as they were quizzed about the rights negotiations,including Mr McWilliam as well as former Nine Entertainment boss David Gyngell and former Network Ten boss Hamish McLennan.
On Friday,Justice Jonathan Beach threw out the majority of the case against Mr Mitchell but found he did breach the law but on"a narrow basis only". Justice Beach also completely dismissed the case against Mr Mitchell's co-accused Mr Healy.
Justice Beach did find Mr Mitchell acted improperly when forwarding internal Tennis Australia emails to Mr McWilliam and disclosing elements of internal deliberations including that he had"stamped on"Tennis Australia chief executive Steve Wood when he suggested the possibility of awarding the rights to another network.
"Mr Mitchell stepped over the line in his dealings with Mr McWilliam,"Justice Beach said.
"And his overall conduct had the tendency to undermine the stance and approach of Mr Steven Wood,the CEO. There were some things that he communicated with Mr McWilliam that he ought not to have done particularly in the latter part of 2012,"Justice Beach said.