| Manager | From | To | M | W | D | L | Win % | Honours and achievements | Notes |
| John Goodall | May 1903 | May 1910 | 253 | 91 | 64 | 98 | 35.97 | Southern League Second Division champions, 1903–04United League Champions, 1905–06 | |
| Harry Kent | May 1910 | May 1926 | 484 | 187 | 121 | 176 | 38.64 | Southern League First Division champions, 1914–15Southern League First Division runners-up, 1919–20 | |
| Fred Pagnam | May 1926 | May 1929 | 133 | 49 | 28 | 56 | 36.84 | — | |
| Neil McBain | May 1929 | August 1937 | 364 | 152 | 77 | 135 | 41.76 | — | |
| Bill Findlay | August 1937 | February 1947 | 114 | 50 | 25 | 39 | 43.86 | Football League Third Division South Cup, 1937 | |
| Jack Bray | March 1947 | January 1948 | 40 | 11 | 10 | 19 | 27.50 | — | |
| Eddie Hapgood | February 1948 | March 1950 | 95 | 32 | 29 | 34 | 33.68 | — | |
| Ron Gray | March 1950 | August 1951 | 56 | 13 | 15 | 28 | 23.21 | — | |
| Haydn Green | August 1951 | October 1952 | 64 | 21 | 14 | 29 | 32.81 | — | |
| Len Goulden | November 1952 | October 1955 | 143 | 54 | 41 | 48 | 37.76 | — | |
| Johnny Paton | October 1955 | February 1956 | 17 | 3 | 6 | 8 | 17.65 | — | |
| Len Goulden | February 1956 | July 1956 | 17 | 6 | 3 | 8 | 35.29 | — | |
| Neil McBain | August 1956 | February 1959 | 131 | 44 | 35 | 52 | 33.59 | — | |
| Ron Burgess | February 1959 | May 1963 | 220 | 92 | 50 | 78 | 41.82 | Football League Fourth Division promotion, 1959–60 | |
| Bill McGarry | July 1963 | October 1964 | 68 | 29 | 21 | 18 | 42.65 | — | |
| Ken Furphy | November 1964 | July 1971 | 334 | 132 | 86 | 116 | 39.52 | Football League Third Division champions, 1968–69,FA Cup semi-finalists, 1970, whilst in second flight | |
| George Kirby | August 1971 | May 1973 | 97 | 21 | 27 | 49 | 21.65 | — | |
| Mike Keen | June 1973 | April 1977 | 196 | 73 | 52 | 71 | 37.24 | — | |
| Graham Taylor | June 1977 | May 1987 | 527 | 244 | 124 | 159 | 46.30 | Football League Fourth Division champions, 1977–78Football League Third Division runners-up, 1978–79Football League Second Division runners-up, 1981–82Football League First Division runners-up, 1982–83FA Cup runners-up, 1983–84FA Cup semi-finalists, 1987 | |
| Dave Bassett | May 1987 | January 1988 | 28 | 7 | 8 | 13 | 25 | — | |
| Steve Harrison | January 1988 | March 1990 | 115 | 40 | 36 | 39 | 34.78 | Watford relegated to EFL 2nd division | |
| Colin Lee | March 1990 | November 1990 | 35 | 7 | 10 | 18 | 20 | — | |
| Steve Perryman | November 1990 | July 1993 | 132 | 44 | 37 | 51 | 33.33 | — | |
| Glenn Roeder | July 1993 | February 1996 | 139 | 44 | 40 | 55 | 31.65 | — | |
| Graham Taylor | February 1996 | June 1996 | 18 | 5 | 8 | 5 | 27.78 | — | |
| Kenny Jackett | June 1996 | June 1997 | 55 | 20 | 20 | 15 | 36.40 | — | |
| Graham Taylor | June 1997 | May 2001 | 202 | 79 | 52 | 71 | 39.11 | Football League Second Division champions, 1997–98Football League First Division play-off winners, 1998–99 | |
| Gianluca Vialli | May 2001 | June 2002 | 52 | 20 | 11 | 21 | 38.46 | — | |
| Ray Lewington | June 2002 | March 2005 | 150 | 51 | 39 | 60 | 34 | FA Cup semi-finalists, 2003, whilst in second flight | |
| Aidy Boothroyd | March 2005 | November 2008 | 176 | 65 | 51 | 60 | 36.93 | Football League Championship play-off winners, 2005–06,FA Cup semi-finalists, 2007 | |
| Malky Mackay (caretaker) | November 2008 | November 2008 | 5 | 2 | 1 | 2 | 40 | — | |
| Brendan Rodgers | November 2008 | June 2009 | 31 | 13 | 6 | 12 | 41.93 | — | |
| Malky Mackay | June 2009 | June 2011 | 99 | 33 | 25 | 41 | 33.33 | — | |
| Sean Dyche | June 2011 | July 2012 | 49 | 17 | 17 | 15 | 34.69 | — | — |
| Gianfranco Zola | July 2012 | December 2013 | 75 | 33 | 15 | 27 | 44 | — | — |
| Giuseppe Sannino | December 2013 | August 2014 | 36 | 15 | 9 | 12 | 41.67 | — | — |
| Óscar García Junyent | September 2014 | September 2014 | 4 | 1 | 2 | 1 | 25 | — | — |
| Billy McKinlay | September 2014 | October 2014 | 2 | 1 | 1 | 0 | 50 | — | — |
| Slaviša Jokanović | October 2014 | June 2015 | 36 | 21 | 5 | 10 | 58.33 | Runner up in the 2014–15 Football League Championship, promotion to English Premier League | — |
| Quique Sánchez Flores | June 2015/September 2019 | May 2016/December 2019 | 56 | 18 | 13 | 25 | 32.14 | Took Watford to the semi-final of the 2015–16 FA Cup | — |
| Walter Mazzarri | July 2016 | May 2017 | 41 | 12 | 7 | 22 | 29.27 | — | — |
| Marco Silva | May 2017 | January 2018 | 26 | 8 | 5 | 13 | 30.77 | — | |
| Javi Gracia | 21 January 2018 | 7 September 2019 | 66 | 25 | 13 | 28 | 37.88 | Took Watford to the final of the 2018–19 FA Cup | |
| Hayden Mullins (caretaker) | December 2019 | December 2019 | 2 | 0 | 1 | 1 | 0 | — | — |
| Nigel Pearson | December 2019 | July 2020 | 22 | 7 | 5 | 10 | 31.82 | — | — |
| Hayden Mullins (caretaker) | July 2020 | July 2020 | 2 | 0 | 0 | 2 | 0 | Watford relegated to EFL Championship | — |
| Vladimir Ivić | August 2020 | December 2020 | 22 | 9 | 8 | 5 | 40.91 | — | — |
| Xisco Muñoz | December 2020 | October 2021 | 36 | 21 | 4 | 11 | 58.33 | Watford promoted to Premier League | — |
| Claudio Ranieri | October 2021 | January 2022 | 14 | 2 | 1 | 11 | 14.29 | — | — |