Monteiro made her marathon debut in 2008 and finished fifth at the Rotterdam Marathon. She is the most successful athlete at the Cidade de Ovar Half Marathon, having won the competition six times. She represents Maratona Clube de Portugal in club competitions.
Born in Ramela, Guarda, Portugal, Inês Monteiro first experienced success in professional athletics at cross country competitions: she won the silver medal in the junior race at the 1998 European Cross Country Championships and took the gold the following year. On the world stage, she reached the 5000 metres final at the 1998 World Junior Championships in Athletics and competed in the junior race at the 1998 IAAF World Cross Country Championships. She improved her position for the 1999 edition in Ireland, finishing in thirteenth.
She progressed to senior races in 2000, competing in the short race at the World Cross Country Championships and winning the Cidade de Ovar Half Marathon in 1:12:24. She finished seventh at the 2001 European Cross Country Championships but she won a gold medal as part of the best performing team. Track running became her focus in 2002, but she failed to make the 3000 metres final at the 2002 European Athletics Indoor Championships and finishing in 12th in the 5000 m final at the 2002 European Athletics Championships. However, she guided her team at the 2002 European Cross Country Championships to a silver team medal. At the World Student Games that year she managed to win bronze in the cross country. A second win at the Ovar Half Marathon in October was soon followed by a win in Azambuja which made her the 15 km national champion.
She did not break into the top thirty at either the 2002 or 2003 World Cross Country Championships. She represented Portugal at the Olympics for the first time at the 2004 Athens Games. Running in the 5000 metres, she performed poorly and finished 18th with 16:03.75 – fifty seconds slower than her best that season. After finishing just outside the top 25 runners at the 2005 World Cross Country Championships, she experimented with a switch to the steeplechase. She finished in 13th place in the 3000 m steeplechase at the 2005 World Championships in Athletics. The next two years saw her career stall: after a poor 64th-place finish in the World Cross Country Championships she ran infrequently and only returned to competition in mid-2007.
Monteiro showed much improvement in the 2008 season. She ran her fastest ever time at the World Cross Country Championships (27:12) and took fifth place at the Rotterdam Marathon – her first competitive outing over the distance. She qualified to represent Portugal at the 2008 Beijing Olympics but she did not manage to finish the Olympic marathon race. She closed the year on a positive note, however, winning the Ovar Half Marathon for a fourth time, and taking individual bronze and team gold at the 2008 European Cross Country Championships. She closed the season by beating Olympic silver medallist Eunice Jepkorir to win the Cross Internacional de Venta de Baños.