Donnellan first came to prominence as a member of the talented
St Jarlath's College in
Tuam team of the early 1990s. He played a crucial role in their
Hogan Cup–winning season of 1994 alongside future Galway teammates
Declan Meehan, Tomás Meehan,
John Divilly, Tommy Joyce and
Pádraic Joyce. They reached the Connacht final the following year but lost out to their biggest rivals,
St Patrick's College, Tuam. He would later once more play alongside Joyce with the
Tralee IT team that won the 1998
Sigerson Cup.
Senior In 1998, Donnellan won his first
All-Ireland SFC medal as part of the
Galway side that won the
1998 championship. During the first half of the final against
Kildare, Donnellan picked up the ball inside the heart of his own defence and proceeded to go on an amazing run, soloing the length of the field while exchanging a one-two with
Kevin Walsh in midfield. As he approached the Kildare goal, he laid the ball off to
Derek Savage, who passed to
Seán Óg De Paor. De Paor slotted the ball over the bar. The score re-invigorated the Galway team, who were losing at the time. Donnellan's overall performance inspired Galway to their first football title in 32 years and completed a unique hat-trick of senior All-Ireland medals for his family, as he followed in the footsteps of his father John (1966) and his grandfather Mick (1925). The final score was 1–14 to 1–10. That solo run was later voted No.1 in the
Top 20 GAA Moments in 2003. Donnellan was named
Texaco Footballer of the Year that year. After reaching another
All-Ireland SFC final in 2000, lost to
Kerry after a replay, Donnellan and Galway won the
2001 All-Ireland SFC title. After losing to
Roscommon in the Connacht SFC semi-final, Galway entered the newly introduced back-door qualifiers and defeated
Wicklow,
Armagh and
Cork to reach the All-Ireland SFC quarter-finals. They gained revenge over Roscommon with 0–14 to 1–5 victory to reach the All-Ireland SFC semi-final, where they defeated
Derry by three points. In the
2001 All-Ireland SFC final, they outclassed a
Meath team by 0–17 to 0–08.
Club Donnellan had a high-profile transfer to the
Salthill–Knocknacarra club in 2005. He soon won an
All-Ireland Senior Club Football Championship with his adopted club. He gave a man-of-the-match performance in the 2005 final, where Salthill narrowly edged out
Antrim GAA club
St Gall's. ==Soccer==