Peyton Manning completed an NFL record 450
pass completions in 2010.
Tommy Maddox
Through the 2008 season, that is 298 by Tommy Maddox in 2003.
Fran Tarkenton who had 3,686 career completions. Marino passed him in the 1995 season.
According to Pro Football Reference, as of the start of the 2008 season Brady has 2294 completions in the regular season and 372 completions in the playoffs.
According to Pro Football Reference, as of the start of the 2008 season Manning has thrown 3,468 regular season completions and 323 completions in the playoffs.
The stats for Brett Favre's rookie season, 1991, are 0 completions in 5 pass attempts for 0 yards and 2 INTs.
There was no rating system used by the NCAA in 1974 ... that wasn't instituted until 1979. The 'passing leader' was considered the QB with the most completions for the season. In 1974, that was Steve Bartkowski of the University of California with 182 completions.
The person that holds the record for the most completed passes in a game is Drew Brees. He completed 45 passes in an overtime game in 1994. The most passes completed without going into overtime belongs to Rich Gannon, who threw 43 completed passes.
In the 2006 season Tony Romo had 220 completions in 337 attempts (65.3% completion percentage) for 2,903 yards. He played in all 16 games and started 10. As a starter, his record that year was 6-4.
Brett Favre, who holds virtually every career record for a quarterback, had 6,300 lifetime pass completions.
Highest completion percentage in a post season game (92.86% January 12, 2008), most passing touchdowns in a season (50 in 2007), most completions in a Super Bowl (32 in Super Bowl XXXVIII), most completions in a Super Bowl career (100), and is one of only three others to win multiple Super Bowl MVP's (Joe Montana has 3, Bart Starr has 2, and Terry Bradshaw has 2).
Joe Montana