The baroness, who chaired a commission reviewing child safeguarding policies of the Church in England and Wales in 2007, will chair a panel including Dr Valerie Brasse, an adviser to the earlier Cumberlege inquiry, and Sir Cyril Chantler, former chairman of Great Ormond Street Hospital for Children.
The British knights have been accused of shortcomings when dealing with concerns about a sacristan and companion of the order who has been convicted of child pornography offences.
Vernon Quaintance, 68, served at the knights' weekly Masses at their church at the Hospital of St John and St Elizabeth, in St John's Wood, north London.
In a separate police investigation, he has been arrested and bailed in connection with seven allegations of indecent assault dating between 1970 and 2011.