The 55-year-old Italian, who arrived in July to replace Quique Sanchez Flores - also sacked after one season in charge - said he had no regrets.
Sunday's home game against Manchester City will be his last in charge.
"We got the magic 40 points, the objective of the season, with six games left," he said.
Mazzarri began Friday's news conference with a 14-minute prepared statement, thanking fans and players and reiterating the team had achieved what it set out to do.
Before his dismissal was announced, reports suggested he had fallen out with some players, including captain Troy Deeney.
When asked about that, Mazzarri said: "Deeney is a player who scored more than last year, he played a lot this year, and he helped the team reach the 40 points. This is what counts for me, nothing else."
Watford could finish as high as 11th in the Premier League with a win on Sunday but Mazzarri said it could have been better.
"Never in my career have I had so many injuries in one season," he said.
"There were some games I did not even know who to put on the pitch. But, honestly, I don't have any regrets."
He said it was the right decision for the club to make an announcement on his future before the end of the season.
However he denied claims his lack of English had been a problem this season, and cited the example of Tottenham boss Mauricio Pochettino, who also started his coaching career in England without speaking the language and "took two years to learn" it.
Monday's 4-3 defeat at champions Chelsea was Watford's fifth loss in a row since a 1-0 win over Swansea all but secured their Premier League safety.
Since that home match on 15 April, the Hornets have slipped from 10th to 16th.
Flores left despite taking Watford to the FA Cup semi-finals and comfortably retaining their Premier League status, while predecessor Slavisa Jokanovic exited a year earlier after leading the club into the top flight.
Walter Mazzarri strongly defended his record as Watford boss in his first appearance since the club announced he is to leave at the end of the season.