This painting offers a relatively expressive style of portraiture, considering that it was probably produced in the early 17th century. El Greco was unique in his approach as compared to others from the late Renaissance era. That said, he did take elements from the Venetian school, for example, having lived under the region's rule whilst growing up in Crete. Over time he would live in parts of Italy before relocating to Spain, with most of his time spent in Toledo after that point. With Saint Thomas we find tones of blue, green and red which persist throughout his career and remind us of the Venetian influences which fell upon him. Normally he would incorporate these colours into the clothing of his figures, particularly on religious icons such as this. The saint shown here holds his right hand up whilst staring off to our right hand side. Behind him is an entirely neutral background, as found in most of the artist's portraits, as well as those from members of his workshop.

El Greco would complete a large number of portraits of local Spanish figures who would commission him personally, or through an intermediary. Those tended to be traditionally composed, with the sitter standing face on, directly looking at the viewer. In his religious portraits, though, there would be much more activity, with different poses used in order to tell us more about each saintly figure. Although this piece may have been completed by his studio, we find much the same here. The saint's face is somewhat blurred, underlining an expressive style of art in which achieving a photorealistic image was not the main intention. Instead, the expressive brushwork provides more of an impression, or mood, of how the saint might have looked. That alternative approach became more and more popular as time progressed and this helps to explain why El Greco retains such popularity with the general public today.

The Prado Museum's collection came from the Spanish monarchy who decided to allow their possessions to be viewed by the general public. Over time they were persuaded to transfer ownership of the building itself, as well as its contents, to the state. El Greco's name is linked to forty one items within their collection, most of which were produced by he alone. Others, such as this, were linked to El Greco and his workshop, with it being hard to discern their respective roles on each piece. Efforts were made to create a uniform style which allowed assistants to work alongside El Greco and without damaging the master's legacy. Whilst this enabled them to complete many more commissions, it did have the downside for art historians who have struggled to determine with any certainty as to who specifically were involved in some of these paintings. This issue was particularly common in the artist's later years, when he relied on his assistants much more. By this stage he had built a strong reputation within Spain and could take on just as much work as he desired, with no shortage of prospective patrons in demand of his services.