Violence in Mexico has caused a large number of victims, mostly related to the use of firearms (FA). This paper analyses the trend in FA-related mortality in Mexico in the last 15 years and its impact on life expectancy in Mexico, and its 32 states, in the 2001–2003 and 2011–2013 triennia. Based on official reports of deaths and population data, trends in FA-related death rates by age and sex between 2000 and 2013 were analysed; abridged life tables by both sex at national level and for males by state were constructed for each triennium studied. Temporary life expectancy (TLE) and years of life expectancy lost (YLEL) for population aged 0–85 were calculated—using Arriaga’s method—by age group and selected causes (FA-related deaths, diabetes mellitus, malignant neoplasms and traffic accidents) in each triennium. In the period analysed, the FA rate fell between 2000 and 2007, increased markedly between 2007 and 2012 and then decreased slightly; and male FA-related death rates are clearly higher than female rates. Between the 2001–2003 and 2011–2013 triennia, FA-related YLEL increased nationally (from 0.40 to 0.98 years in men, 0.04 to 0.08 in women) and in 30 states for men. In 11 states, the FA-related YLEL in 2011–2013 exceeded one year among males. In 19 of 21 states where TLE declined between the two triennia, the FA-related YLEL increased. In 2011–2013, injury by FA was the leading cause of male YLEL in age group 15–34. YLEL due to firearms among males in 2011–2013 (0.98) was higher than YLEL by traffic accidents (0.56). Variables like “hectares cultivated with marijuana and opiates destroyed by the army”, “confiscated FA” and “index of impunity” play an important role in explaining the inter-state variations in male FA-related YLEL and the observed changes between both triennia. Thus, the increase in the FA-related death rate, especially among young people, is impeding the rise in life expectancy in Mexico. In several states, particularly Chihuahua and Guerrero, mortality caused by FA seems to be the main reason for the decline in life expectancy among males aged 0–85 years.