Short answer. With respect to that activity, generally yes. Article 280 of the Labor Code says any employee who has rendered at least one year of service, continuous or broken, is considered regular for the activity they were employed to do, and remains so for as long as that activity exists.
What the law says
any employee who has rendered at least one year of service, whether such service is continuous or broken, shall be considered a regular employee with respect to the activity in which he is employed and his employment shall continue while such activity exists
Labor Code, Article 280 — Regular And Casual Employment. Read the full provision →
The proviso is the second route, not the first
The one-year rule is a fallback, and it helps to see what it falls back from. Article 280's main test does not count time at all: employment is deemed regular where the employee has been engaged to perform activities which are usually necessary or desirable in the usual business or trade of the employer — and that applies the provisions of written agreement to the contrary notwithstanding and regardless of the oral agreement of the parties. A worker doing core work of the business can therefore be regular from the first day, without waiting out a year. The article excepts two situations: employment fixed for a specific project or undertaking whose completion or termination was determined at the time of engagement, and work that is seasonal in nature where the employment is for the duration of the season. The one-year proviso then catches what is left over — the employment the article calls casual.
The one-year threshold, read carefully
Article 280's proviso ties regular status to service reaching at least one year. It does not require that the year be worked without interruption — the article specifies whether such service is continuous or broken. That word "broken" matters: gaps in your engagement, such as periods between rehiring for the same task, do not automatically restart the count from zero for purposes of this rule.
Regular 'with respect to the activity'
The status this proviso confers is not an unqualified, general kind of regular employment — it is regular status with respect to the activity in which he is employed. That phrase ties your regular status to the specific work you have been doing. If the year you have accumulated was spent on one particular kind of task, the article's proviso speaks to your status regarding that task, not to some broader, undefined role.
It lasts only while the activity exists
The article adds a condition on the back end too: employment shall continue while such activity exists. Regular status under this proviso is tied to the activity continuing to exist within the business, not to a fixed guarantee of employment regardless of circumstances. If the specific activity genuinely ceases to exist in the employer's operations, this proviso's own wording ties the continuation of employment to the activity's own continued existence.
What to gather if your status is disputed
If you believe this proviso applies to you, the practical work is adding up your actual time doing the same activity, across every period you worked it, whether or not the engagement was continuous. Keep records of your start and end dates for each stint and what the work actually involved, since that is what determines whether the one-year threshold has been met. A lawyer can help you assess whether your combined service and the nature of your work bring you within this rule.