“The protection of the integrity of the judicial process requires that an expert witness be immune from civil suit by any person with whom his or her only relationship derives from the judicial proceeding: Varghese v. Landau (2004), 2004 CanLII 5084 (ON SC), 3 R.F.L. (6th) 204 (Ont. S.C.), at para. 48; Carnahan v. Coates (1990), 1990 CanLII 2299 (BC SC), 71 D.L.R. (4th) 464 (B.C.S.C.), at p. 474; Howatt v. Klassen (2005), 31 C.C.L.T. (3d) 54 (Ont. S.C.), at paras. 11 and 15, citing Fabian v. Margulies (1985), 1985 CanLII 2063 (ON CA), 53 O.R. (2d) 380 (Ont. C.A.).
Immunity from suit extends not only to reports filed in court and oral evidence given in court, but also to activities outside of court related to a report or its preparation: Varghese v. Landau, at para. 49; Smith (next friend of). v. Kneier, 2001 ABQB 291, 288 A.R. 144, at para. 11, citing Evans v. London Hospital Medical College [1981], 1 All E.R. 715 (Q.B.).
The protection is absolute. Even allegations of bad faith are insufficient to remove the application of the immunity doctrine: Howatt v. Klassen, at paras. 11-13, citing Samuel Manu-Tech Inc. v. Redipac Recycling Corp. (1999), 1999 CanLII 3776 (ON CA), 124 O.A.C. 125 (C.A.).
One of the justifications for immunity is the protection of the court process, which seeks to discourage relitigation of issues: Smith (next friend of). v. Kneier, at para. 14. This is especially important in the family law context, which is already fraught with conflict. In the family law context, attempts to sue expert witnesses have been dismissed or struck out at early stages because of immunity: e.g. Van de Vrande v. Butkowsky, 2010 ONCA 230, 99 O.R. (3d) 648; Carnahan v. Coates; Howatt v. Klassen; Varghese v. Landau; Smith (next friend of) v. Kneier.”