Fanning and McHale built the Expos from scratch; in those days, prior to the era of free agency, newly formed clubs could only rely on expansion and amateur drafts and trades to build their talent base.

In the 1968 NL expansion lottery, Fanning drafted veterans such as Jesús Alou, John Bateman, Donn Clendenon, Larry Jackson, Mack Jones, Manny Mota and Maury Wills, and young players like Jack Billingham, Skip Guinn, Carl Morton and Bill Stoneman.

He was forced to improvise when veteran pitcher Jackson, a five-time All-Star and winner of 194 career games, decided to retire rather than report; Fanning accepted shortstop Bobby Wine as compensation.

Entering their fourth season in 1972, Fanning reshaped the Expos through another headlining transaction, trading Staub to the Mets for three young regulars – shortstop Tim Foli, outfielder Ken Singleton and first baseman Mike Jorgensen.

In the mid-1970s, the Expos began to harvest players from their farm system, including Steve Rogers (1973), Barry Foote (1974), Gary Carter, Larry Parrish and Ellis Valentine (1975), and Warren Cromartie and Andre Dawson (1976).

After the 1975 season, McHale and Fanning promoted Triple-A manager Karl Kuehl, who had overseen the development of many of the younger players,[4] to replace Mauch at the Expos' helm.

However, when Montreal regressed in 1976 and fell back into the NL East cellar, Fanning was reassigned by McHale to a player developmental role and succeeded as general manager by Charlie Fox.

Fanning's calm and easygoing style favorably contrasted with Williams' hard edge, and the Expos won 16 of their last 27 games to capture the second-half NL East title, thus qualifying for the playoffs per 1981's strike-shortened, split-season format.

After a brief stint as a color commentator on Expos radio and TV broadcasts, Fanning left the Montreal organization, working next as a scout for the Colorado Rockies prior to becoming an assistant general manager and then ambassador to amateur baseball/Canada for the Toronto Blue Jays.