His father, an Irish immigrant who was a railroad worker, died in 1944; his mother worked at the California Department of Motor Vehicles.

[3][4] A right-handed batter and thrower who stood 5 feet 10 inches (1.78 m) tall and weighed 175 pounds (79 kg), in his playing days he was a peripatetic, weak-hitting catcher who originally signed with the St. Louis Cardinals organization in 1951.

After helming the Triple-A Dallas Rangers in 1964, he won Southern League pennants at Kansas City's Double-A affiliates, Mobile (1966) and Birmingham (1967), where he groomed many future members of the Oakland Athletics' early-1970s dynasty — including Hall of Famers Rollie Fingers and Reggie Jackson, as well as Sal Bando, Blue Moon Odom, Joe Rudi and others.

The Padres improved incrementally, winning 60, 71, and 73 games through 1976,[9] then signed free agents Fingers and Gene Tenace away from McNamara's old team, the A's.

He spent 1978 as a coach for the California Angels, then was hired to succeed Sparky Anderson, also a future Hall of Fame manager, as skipper of the Cincinnati Reds in 1979.

[11] McNamara's 1979 Reds, minus legend Pete Rose, who had defected to the Philadelphia Phillies as a free agent, won 90 games—two fewer than Anderson's 1978 team.

After the 1982 season, when the Angels lost a heart-breaking ALCS to the Milwaukee Brewers, their veteran manager, Gene Mauch, retired.

[12] The following year, the 1984 Angels clawed back to .500 at 81–81, but came within three games of the division champion Kansas City Royals, who won only 84 contests all season.

[14] Late in the year, he moved John to the bullpen, then forbid him to practice throwing because he wanted to keep the pitcher's arm fresh in case he needed him.

With Mauch ready to return to the dugout, the Angels agreed to let McNamara go to Boston, and in 1985, he led the Red Sox to another .500 season; but at 81–81, they finished 181⁄2 games behind the Toronto Blue Jays in the American League East Division.

McNamara was also criticized for pinch-hitting Clemens with rookie Mike Greenwell, who struck out on three pitches, when veteran slugger and noted cluch hitter Don Baylor was also available.

[21] With Game 7 delayed a day due to rain in New York, McNamara bumped originally-scheduled starting pitcher Oil Can Boyd in favor of starting Bruce Hurst, the winner of Games 1 and 5 and the presumptive MVP of the series if the Red Sox were to win, on three days' rest; the Red Sox had chosen to go with a normal four-man rotation during the series, unlike the Mets who pitched a three-man rotation.

The decision upset Boyd so much that he began drinking heavily afterward and drank himself to the point of intoxication, according to accounts given by McNamara and his pitching coach Bill Fischer, thus rendering him unavailable.

[22] Hurst was staked to a 3–0 lead and pitched shutout ball for five innings, but tired in the sixth allowing the Mets to score three runs to tie the game.

Since Boyd's actions had left the bullpen short staffed in a situation where every able pitcher would need to be available in case of an emergency, McNamara decided to bring Calvin Schiraldi in despite his struggles in Game 6 and the fact that he was still tired from pitching 2.2 innings that night (something he wasn't used to).

McNamara was invited to return for 1988, and the Boston bullpen was buttressed by the acquisition of All-Star relief pitcher and future Hall of Famer Lee Smith.

[26] McNamara returned to the Angels' organization as a minor league catching instructor, but was called to manage in the majors a final time in 1996 at age 64.