Mehl began his ministry service in June 1966 as a representative of LIFE Bible College, and became the Youth Pastor at the Portland Foursquare Church in September 1966.

By 1969, he was serving as the youth director for the Great Lakes District in Kenosha, Wisconsin.

Over the next 30 years, however, attendance on Sundays grew to over 6,000 people, resulting in the largest church congregation in Oregon in 1999.

While still senior pastor at Beaverton, the board of regents of LIFE Bible College called upon Mehl to serve as interim president, a position which he held from July 1992 until August 1994.

[3] He was also recognized as one of a handful of pastors helping the Foursquare church experience large growth in the 1970s.