Former Mayer Brown partner Joseph P. Collins was sentenced yesterday to serve seven years in prison for helping Refco Inc. executives defraud investors of $2.4 billion—crimes the judge said were motivated by “excessive loyalty” to his client.

Mr. Collins, 59, of Winnetka, Ill., who had sought a sentence of mostly community service, shook his head as Southern District Judge Robert P. Patterson said that “the significance of what transpired here is the reason for the sentence.”